Basic Information:

Electrical Diagnostic Supplies. [Editor] To assist in diagnosing and repairing electrical problems, consider acquiring:

Wiring Diagrams Website.

[Editor] See http://www.autoelectric.ru/auto/volvo/740/1989/740-89.htm for some scanned OEM wiring diagrams of selected 740, 940 and 960 cars. These are limited; you should purchase, as one of your first manuals, an OEM wiring diagram book from Volvo.

Electrical Diagnosis Tips

For a superb introduction to basic automobile electrical diagnosis using a digital multimeter and accessories, see Fluke Corporation's website reference at http://www.fluke.com/application_notes/automotive/beatbook.asp?AGID=1&SID=103

Wiring Fault Diagnostic Tips

[Tips from Import Car Magazine]
DIAGNOSTIC THOUGHTS
Wiring failures occur as open, shorted or short-to-ground (grounded) circuits. An open circuit, obviously, is a broken or disconnected wire. Shorted circuits occur when the insulation between two wires fails. Grounded circuits occur when a bare wire is allowed to touch the vehicle's powertrain, sheet metal or frame. As for narrowing diagnostic probabilities, let's remember that:

1. Before wasting hours of expensive diagnostic time, test all fuse circuits with a DVOM or approved test light. Remember that fuses can fail without showing signs of an obvious burn-through. Since a loose or corroded fuse connector may also cause many intermittent circuit failures, thoroughly inspect and clean the fuse circuits before proceeding with your diagnosis.
2. Most wiring failures occur at either end of the wire as a bad connection. Although splice failures inside the wiring harness are rare, some nameplates are notorious for splice failures. Technical service bulletins (TSBs) and Internet sources offer valuable insight to typical nameplate problems.
3. Corroded harness connections cause most intermittent circuit failures. Simply unplugging the connector and applying an electrically compatible corrosion inhibitor will repair most connector failures
4. When diagnosing intermittent failures, remember that suspect turn signal flashers, fuses, bulbs and relays can be replaced more cheaply than they can be diagnosed. When diagnosing an intermittent lighting failure, for example, I always begin by cleaning the bulb sockets and installing new bulbs. How much diagnostic time are you willing to spend testing a $0.98 light bulb that's nearing the end of its practical service life?
5. Engine, computer and body ground connections should be checked first, especially if the vehicle has recently visited the collision repair shop.
6. Keep in mind that most electrical systems, when left untouched, perform very reliably. When they do fail, the failure will be predictable, such as a bad current or ground connection, blown fuse and the like. Most predictable failures can be solved within a two-hour time block.
7. On the other hand, the DIY mechanic "short-testing" a cooling fan switch or fuel pump relay can create a multiple failure with unpredictable consequences like burning a wire within a wiring harness. Obvious tampering should always create a red flag... Electrical "red flags" may include newly installed sound systems, electrical accessories, trailer brakes, auxiliary lighting and the like
8. Many circuits serve more than one accessory or function. Years ago, for example, I found that a burned brake light fuse was caused by a loose courtesy light in the ashtray. Without a good magnetic short detector, the problem would have been difficult to solve since a relationship between a brake light and ashtray light isn't immediately logical or clear, to say the least. In other unlikely cases, I've found an instrument cluster fuse that also supplies field current to the alternator. The moral is, never rule out the effect of one circuit upon another
9. In fact, avoid using test lights altogether. When testing fuses, for example, I use an LED-type test light (available from a major tool manufacturer) that indicates open or grounded fuse circuits and voltage availability. This eliminates guesswork and protects ground-sensitive electronic circuits like air bag sensors.
10. Use a professional DVOM with a min/max voltage feature and alarm to test intermittent failures. The min/max feature will record the highest voltage reached in the circuit and sound an alarm each time a higher voltage is reached. For the technician working alone, this feature is a real time saver, especially when performing a "wiggle" test on an intermittent wiring problem. In the same sense, lab scopes are particularly useful to find loose ground connections. During a wiggle or vibration test, loose ground connections will show up as a voltage spike in an otherwise zero-volt lab scope waveform.
11. Remember how hard it is to find the trim screw driven through a wiring harness hidden underneath a headliner? A good short detector will help you quickly locate concealed short-to-ground circuits. For about 30 bucks, it's a great time saver for you and your customer alike.
12. Tips on Finding Open Circuits. An open circuit is the opposite from one that is "shorted", because it is similar to a cut wire that is not connected to anything. This can be tricky to find since in an "open" circuit, there is no electricity flowing to help you locate the spot with a meter or short finder. This diagnostic trick uses the car's radio and any device with a large LCD display like a calculator to find an open circuit, but only if the car's antenna mast is metal. Let's say the brake lights are inoperative due to an open positive feed from the brake light switch. You have already found the wire to be open somewhere by an ohm meter test, but you don't know where and would like to shorten the search. Before you go ripping the carpet and interior trim out of the vehicle looking for the broken wire, grab your calculator. Start by disconnecting both ends of the line (unplug the lights end and the brake light switch then consult a wiring diagram to make sure any other devices attached to that circuit are disconnected). Connect an insulated jumper wire between the antenna mast and one end of the offending wire. Tune the car radio to a quiet (unused) AM channel. Turn on the device you are using with the LCD display (like your calculator) and pass it down the offending wire. You will hear the "Radio Frequency" noise generated by the LCD display in the car's radio speakers as you pass the good sections of wire and will fade out as you pass the break. You can demonstrate this test by tuning any radio to a quiet AM station and passing an LCD display device over the antenna.
13. Tips on Finding Short Circuits. See the Special Tools section of the FAQ for suggestions on tools capable of rapidly locating shorts in wiring harnesses

Fuse Locations.

See the following diagrams for fuse locations in 740/940 and some 760/all 960 cars:

740/940 Fuse Locations 960 Fuse Locations

Relay Basics. For a good site explaining the basics of relays, see Basic Car Audio Electronics.

Relay Locations.

See the illustrations below left and middle to identify relays in 740/940 cars. Caution: relay locations vary by model, year, and market: to determine differences, use an OEM wiring diagram book. To access relays, remove the ashtray (push the spring clip at the top) and fuse panel cover (push the plastic snap at the bottom). Then remove the snap-on cover over the cigarette lighter with your fingernail or a small screwdriver. Remove the two philips screws securing the storage box: one of these is angled in. Remove the storage box by gently tugging on the left side, pulling it and the cigar lighter wire out from the console. Beneath it you will see the relay tray behind the fuses. For 760/960 cars, starting in the 1988 model year the relays are mounted under the left hand console panel, just the the left of the front passenger's left knee. Pull gently on the panel and it will unsnap. See the right illustration. Beginning in 1995, 960 cars have relays in the engine compartment and in the fuse panel shown above. 1994/1995 940 B230FD non-turbo cars using either Bosch or Regina have rather square, squat, blue-colored fuel injection relays in the front row, second from right.

Relay Removal.

[SGFM] Relays in most cars pull straight up from the relay base. However, in some 760 models (with relays located behind the lower dash panel below the stereo, facing the passenger side) the relays have retention devices. Two sides of each relay are held by plastic clips that must be pried OUTWARD at the same time to allow removal of the relays. Unless you accomplish this maneuver, you'll either break the relay or the retention device when forcing the relay out. I found that toothpicks wedged into each side retention device allowed the relay to be removed with the least amount of pain. In the 760/960 diagram shown above, A, B, F, J, L, and M are permanently attached to the board.

Air Conditioning Relay. [Inquiry] The 700/900 FAQ shows the relay cluster, but there is no AC or ACC relay shown on this panel. Where is it? [Response] Check your wiring diagram. If an air conditioning relay is fitted, it generally will be located behind the glovebox.

Relays and Fuses:

Fuel Injection Relay Applications.

FI relays can differ by model. According to the Pocket Date Book from Volvo, all F/T engines (both Bosch and Regina systems) through 1993 use the -608 white relay regardless of turbo/non-turbo. For 1994 and after, B2XXF NA-engines use the -270 relay and T turbos use the -608 relay. All E engines use the -639 relay. However, some 760 Turbos use the green 1362914 relay. Per John Marshall in New Zealand, some of the later 9 series (1994 onwards) have a different layout of relays and use a blue Hella fuel pump relay, mounted second from the right in the front row. The one to the right of it is the same Hella relay, used for high beam lighting. The Hella relays on have 5 pins in the base and are marked as follows: Hella 12V/ 4RD/ 003-520-52. Even a diligent search of Volvo Technical publications (e.g., the wiring diagram, that for other electrical equipment, etc.) will not show this change in the color, size, and location of this relay (versus the white, rectangular, second-row position, for earlier 940s). Note that relays are not interchangeable.

Relays and Fuses Overheating. Relays.

The fuel injection relay should not get hot even if the pump is drawing too much current...until the excess current starts to kill the contacts. Either way, a hot relay is a bad relay. There are three possible reasons for a hot relay:

Resoldering Internal Relay Solder Joints.

All mean that a point in the relay has resistance and when current flows through that point there will be a voltage drop which means work is being done and that work manifests itself as heat (P = E * I). Over time the bad joint gets worse due to the heat and maybe heat/cool cycles, the resistance goes up, the joint gets hotter, the voltage at the pump goes down so it needs more current to do the same work so the joint gets hotter, it gets worse, well you get the picture. At its worst this kind of scenario can destroy a motor because the low voltage condition causes a high current draw which over heats the motor. The relay may or may not be fixable. I usually try to fix them and am often successful. Note that Volvo released an improved relay, which has silver base terminals, to solve this problem. If the car's existing relay has copper-colored terminals, replace it with the newer relay. [Another:] Your description of the innards of the fuel pump relay sounds right.... the wires from the solenoid coils to the PCB are small and fragile -- but I've never experienced them breaking (at least, breaking from vibration). Because they're fragile, fingers off! Soldering the PCB is done on the other side from the components. You'll notice the component leads (including the fine wires) stick through and are soldered to so-called "traces". These traces are copper, but are usually completely covered by solder so have a silvery color. You'll also see where larger tangs stick through and are soldered -- these are the heavy-current leads from the relay contacts as well as the relay connectors. I usually solder the heavy connections using a soldering gun (but carefully, because these deliver a lot of heat quickly, and can damage a PCB). The smaller solder connections are best done with a small 25-Watt iron. Of course, you must use electronic solder, not plumbing solder (which contains an acid-based flux).

Soldering the Relay Base Crimped Connections.

I've seen several instances on 740s of excessive contact resistance at the fuel pump relay base connector. This causes overheating and melting of the spade connectors and plastic socket. It probably wouldn't hurt to examine the male spade connectors and socket for signs of high resistance and overheating (discoloration of metal, melted or burned plastic). [UK Club] The problem seems to be poor connectivity at the terminal end of the wire. Over time, the factory crimped wire and relay base connector increased in resistance and overheats. I eliminated the problem by soldering the wire and connector to correct or reduce resistance heat. Unplug the relay. Pull up the base and cut back the wire insulator just slightly. Prepare the surface areas and solder a bridge between your wires and connectors. You do not have to put on new crimped connectors. Re-insulate the exposed areas with a liquid insulator. Install the relay. Crimp Integrity. [Rick Taylor] After my wipers and heater stopped working, I took the fuse panel cover out and discovered that for the relevent fuse, Volvo uses one hot wire for three fuse positions. This single hot wire fed the blower, wipers and the SRS system fuses! It was loose under the panel and I re-crimped the contact to make it fit tighter. This seems to have solved the problem. 940 Electrical System Shutdowns. [Al Bert] If the car's electrical system shuts down and the battery cables and ignition switch are not at fault, check the relay/fuse panel mains and sockets, especially what may be a hot wire connected to the short buss below the sockets. Fuses 1 through 5 share a common battery feed; if this overheats or the sockets melt, similar symptoms will appear. Often this will be intermittent: when the wires cool down, the connection is re-establised. Burnt fuse and relay panels and overheated connections are common in used 740 and 940 cars.

Drilling Holes in Relay Covers to Cool Them.

Problems with the 740 fuel pump and headlight relays are well documented. Volvo has a tech. bulletin that recommends replacement of the relays and the sockets, which have both been done to my car before I purchased it. Driving today, I put my finger on the fuel pump relay and it was darn warm. I could just hold my finger on it - any hotter and I wouldn't be able to. Is this normal/acceptable? If no, what's the fix (another relay??). [Response:] Relays on Volvos run hot. That's why I drill holes in the covers. You must first remove the circuit board to drill the cover. On overdrive relays, I have never had to replace a relay with holes in it, it seems to help a lot. I have also run cooling to the relay/fuse board from the crotch cooler port, so when the A/C is on, it blows cool air on the board via hose. It may help and can't hurt.

Socket Integrity .

[Bob Kraushaar] If a relay/fuse is not firmly set in its socket, a poor contact can result, which results in overheating and melting plastic. If the plastic holding the wire connectors melts/softens enough, the connector can be pushed out of the retainer and make contact with nearby wires or metal parts. This, in fact, happened to my headlight relay with resulting smoke and intermittent light failures.

Relay and Fuse Panel Removal and Replacement .

Preventive Maintenance. [Jim McDonald] Relay and fuse connectors carry a great deal of current. Removing and reseating the fuses and relays every couple of years will ensure that the connections are seated and will also diagnose loose connections prior to failure. Look for evidence of burned fuse or relay holders when you do this.

Removing the Fuse Panel. It is possible to pull the whole relay panel out the front of its opening. Use a good light so you can see well. First remove the plastic storage box (which also contains the accessory socket) above it to facilitate this. The trim around cigarette lighter will pry off to reveal two screws, one going straight in and the other going in at a 45 degree angle. Put your hand below the screws as you remove them as there is a great likelihood that the panel nuts into which the screws are secured will fall out when the screw is pulled out.

To remove the relay tray beneath, look for the white catch on the left towards back of relay panel (back meaning towards back of car). Push this to the left and then lift the relay board up at least 1/2 inch before the tray is pulled rearward and out. If the tray does not side out toward you, the plastic tab might be catching on a side lip of the fuse tray or the spliced and bundled electrical wires running to the back underside of the tray might be catching. Pull gently to allow the wire bundles to unflex as they are removed. The opening in the console is just the right size--the tray does not need to be turned or twisted.The wire umbilical attached to it is long enough to allow the panel to be pulled out quite far. This is also how you can hook up accessories to the fuse and relay connections under the panel.

Replacing the Fuse Panel. [John Sargent] If the airconditioning and heater fan are used much, all 1984-87 760s, and all 740s and 940s (not the 940SE) will eventually wear out the fuse holder for these functions. It is fuse 14 on the early 700 series, and fuse 16 on the later 740s and 940s. The heater fan and AC quit working at all on my daughter's 1987 744T, and the fuse block looked like this. Fuse holder 16 is melted.

I was originally going to bypass fuse 16 with an external fuse holder, but this fuse block was so bad I decided to replace it. Replacing takes a little more time but it isn't hard to do. Get a good fuse block. Disconnect the battery ground before you start. Remove the ash tray, fuse cover, cubby hole, and radio. Then you can lift up on the Central Electric Unit, pull it towards you, and turn it over. Yes, the wires are long enough. They were made to do this.

Everything is color coded to its location. The supply wire for each fuse is in the plastic socket,and is marked with a wrap of black tape. Remember this. Some supply wires feed more than one fuse, as the fuse supply sides are connected inside the fuse block. The supply wire for fuse 16 also supplies fuses 14 and 15 on this car. If you are uncertain, take a picture with a digital camera before you start removing wires.

Once the wires are removed, use a small screwdriver to raise the black plastic over the three lips on the front of the fuseholder. When re-installing the wires, be sure to push them all of the way onto the spade fittings. I use needle nose pliers for removing and re-installing the wires.

Relay Tray Removal and Replacement. My headlight relay got into a bad habit of getting real hot. I had the same problem and after replacing the relay, I replaced the plastic base. It's quite easy, get yourself a Volvo part1307160 (CAD$2.89) and pull your relay/fuse tray out of there. After removing the relay, flip the tray and remove each wire (tape the lug & mark the position). You can usually coerce any crimp-on connectors out by bending the little tab internal to each connector (with a small screwdriver).Once the relay base is clear of wires, unclip and push it out. Install your new base and re-install each wire in the proper position. With crimp-on connectors, you can use a knife to "restore" the little tab on each crimp connector so that it "clicks-in" when you re-install the connector in the base. I find that, It is vital to have firm connectors or else they slide out when you push-in your relay! One additional note... The base melts because there is resistance & arcing between the crimp-on connector and the relay lug. There is quite a bit of current going through there and you want to make sure that you have tight connections. You can do that by "squeezing the gulls" of each crimp-on connector. Contacts #30, 87 & 87b are the culprits (not sure if they are all used though). My relay panel is all plastic. Double-check the part number of the relay base by removing a relay and reading the part number in the center of a "good" relay base.

Crimp Failure. Note that cases of relay or fuse panel socket connector failure have been traced to the crimp on the wire. To solve this, solder the connector to the wire and re-insulate with liquid electrical tape.

Melted Heater Blower Fuse

[Inquiry] My 1984 740 Turbo has a melted fuse that protects the heater blower/ac circuit. The fuse did not blow, but instead heated up enough to melt the fuse and the surrounding fuse box. Suspecting a short to ground fault within the circuit, I have examined the wiring and do not visually see any bare wire. I have replaced the blower motor, relay, and the fan motor switch without solving the problem.

[Response: John Sargent]This can be fuse number 14 (early 740s) or 16. The fuse and fuse holder are simply overloaded in the basic design. There is too much current draw on the fuse holder. It was fine when new, but too many heating cycles weaken the grip of the fuse holder on the fuse after 15 years. This is a very common problem on 700 series Volvos. Unless your car has over 200,000 miles on it, the only part of the central electrical unit that will be bad is the fuse holder for fuse 16. Nothing lasts forever, but fuse 16 is the weak point. The wiring to the CEU should be fine, although high mileage cars can have troubles at other relay sockets. You have two choices:

1. Replace the entire fuse block panel with a new, or good used unit.
2. Buy a new fuse holder and power the AC and heater with it

If you choose option 2, you must pull the central electrical unit out and turn it over. Splice a fuse holder into the lead supplying power to fuse 16. Splice the load side of the new fuse into the black lead supplying power to the heater and AC unit. You must continue to supply power to fuse 16, as fuses 14 and 15 are fed from the supply side of fuse 16. It is possible to intercept those black wires elsewhere, but it is easiest for me at the CEU. If you can get enough slack in the black wire which supplies fuse 16, a red wire nut works great for spicing the new fuse holder in and keeping fuse 16 supplied with power. The fix will be less than $5 US.

Fuse 5 (Clock, Etc.) Failure Diagnostics.

[Tip from R. Duke] I had the classic symtoms of a blown fuse #5 due to a short - lost power to clock, etc. The "ding ding" indicator signal was also constantly sounding. It looks like one of the most common causes is the courtesy/dome light. The circuit board in it can develop a short. The circuit board contains the timing circuit for leaving the light on after you enter the car until you have time to put the key in. Apparently this part has gone through several updates. The internal parts are quite different on the updated one. The new one cost about $78, but it does come with the lenses and bulbs. It actually works better too (better switches). Volvo has a parts bulletin about the change. The new one has a different connector and you are supposed to crimp new pins on each of the 4 wires (Volvo can supply those too). Those pins are hard to crimp unless you have the correct crimp tool, so I just soldered 4 jumper wires on to the circuit board and used insulated spade connectors on the jumper wires to attach to the 4 supply wires. If you ever get this problem. Pull the fuse and take a reading to see which side of the fuse holder has 12 volts on it. Then take an ohm reading from the other pin to ground while you look for the short. That is easier than blowing a bunch of fuses. There are a lot of devices on that fuse.

Repairing and Resoldering Relays.

Here's a generic statement about your relay -- this statement displays my bias about the poor quality of Bosch wave soldering. If you can pop the cover off the relay using a small screwdriver to pry the cover at the edge, try resoldering all the connections on the circuit board before you replace it. (After all, you have nothing to lose but a few minutes.) The heavy connections that go to large components like the actual relay may need a large soldering iron or gun, whereas the connections at smaller components, such as transistors, should be reflowed using a smaller iron, like a 25-Watt iron. Use rosin-core electronics solder. If you're not comfortable soldering, find a friend who is.

[Don Foster:] Over time (like 10 years), the solder used in production manufacturing tends to become crystallized and cracks. The type of solder used in high-volume production is different than that used in an electronics repair shop. The problem with the relays is tiny, almost invisible microscopic cracks in the solder. These cracks usually encircle one (or several) heavy connections, such as from the relay or a main lug connector. Under a bright light, and using a magnifying glass, inspect the soldered connections. Don't forget to look for broken conductive traces as well. Simply resoldering these circuit board very often restores them to perfect performance, and it's a whole lot better (and cheaper) than a $50-$100 replacement part. I have recovered literally dozens of Bosch relays (OD, fuel pump, wipers) to perfect performance this way at $0. In fact, I resoldered ALL the relays in my family's 6 Volvos before a failure stranded us. The illustration shows an overdrive relay with solder cracks. Not shown is a broken trace (discovered with a magnifying glass) at the top of the board, repaired with a soldered jumper wire [courtesy Don Foster] [Murph] It's very helpful when resoldering a relay to treat the pins with some Caig "ProGold" or "Gold Guard Pen". It can go a long way in preventing oxidation. Easy to apply & no waste, but expensive. Any good electronics parts shop will have it

Soldering Tips and Techniques.

[Don Foster] See the excellent Heathkit discussion of how to correctly solder circuit boards and contacts as well as Jay Simkin's tips below.

Overdrive Relays. See the photos above. Other Relays. [Ed Lipe] Relays fail the same way in any early model vehicle: solder joint cracks on the boards. Keep this in mind when you have intermittent problems with any of the relays in your car.

Lamp Failure: Bulb Out Relay.

General. The bulb-out relay senses differential current flows to paired lamps to detect a bulb failure. If it senses a bulb failure, it illuminates the instrument panel warning lamp. However, if the relay itself fails, then the brake lighting circuit (among others) will fail completely and the cruise control will also cease operating.

[Inquiry] The brake lights on this car don't work. The fuse is okay, there is power at the brake pedal switch and the switch works. I get no continuity, power at the white junction block leading to the rear harness. Could it be the bulb failure relay itself or is there a little rats nest in there somewhere. [Response: John Sargent] The brake light failure in our 87 745T was caused by the bulb failure relay. You may be able to re-solder, or you can replace it. The bulb failure relay is in the front left corner of the relay plate, and is red and round. [Self-Diagnosis from Guy Jett] It was the bulb out relay. The counterperson at the local Volvo dealer said "Oh yeah, they go out all the time." Note on diagnostics. It was helpful to disconnect other bulbs and see that the bulb out relay still was not working. I think I will keep a bad bulb or two in the future for such testing. [Jason Kneier] I opened the bulb failure relay up and traced the path the brake light circuits took (pins 54R and 54L on the base of the relay). I saw two suspect solder joints, both of them 'bridging pins' that connected between the three boards, and so I resoldered them and put the relay back in - Success!

Headlamp Failure:

[Inquiry] Driving headlights only work when high beams are selected. Please help. [Response: John Sargent] Are your low beam fuses okay? If they are (and they probably are) you either have a bad high/low switch (unlikely), or a bad Lamp Failure Relay. The Lamp Failure Relay supervises the Low Beams, the Tail Lights, and the Brake Lights, but not the High Beams. Lamp Failure Relays do go bad. Remove the Lamp Failure Relay from it's socket, and test for voltage at the pin connection for terminal 56b, which is one pin clockwise from the pin socket labeled S in the relay base of the Central Electrical Unit. Terminal 56b is the output for low beams from the high/low switch. If you have voltage there, the high/low switch is good on low beams. Re-install the Lamp Failure Relay and test for voltage at the input side the the low beam fuses. If you don't have voltage there, the Lamp Failure Relay is bad. You can pry the cover off and attempt to re-solder it, or get a used one. The headlight relay is energized by the light switch and supplies current to the high/low switch. If it was bad you would only have high beams when pulling the high/low switch towards yourself. In this momentary position, the current for the headlights comes from fuse 2.

Engine Wiring:

Removing Engine Wiring Connectors and Ties .

[Inquiry] What's the trick for removing the Bosch connectors with the wire spring retainers? I know I'm missing something simple here... [Response: R Haire] Depress the spring toward the connector to release the locking action, then pull. It can be frustrating with oily fingers groping under the manifold for the right pinch.

Releasable Wiring Ties. [Carter] The releaseable ties that attach to little posts along the firewall and elsewhere in the engine compartment are Volvo part number 969019/ product number 489492-001 costing about $7.50 for 10.

Baked Engine Relay Connectors.

[Tip from Dick Riess] Son's car decided to have some relay problems. Wasn't the relay, but the plug in ends had turned to mush. After chasing my green manuals, I found the answer. These are instock at Volvo. They are terminals, the insulated kind that insert in various grey connectors, including relays, wiring harness hookups and fuel pumps. These are complete with a pigtale so they can be soldered or crimped together. Volvo number is 3523813-8. Suggested retail is 5.29, got mine for 2.95, so they are reasonable.

Baked Engine Wiring: 700/200 Cars.

[Early-80s to 1987 240 and 7xx cars:] Harness failure often causes multiple symptoms such as rough idling, stalling, hesitation, overall erratic performance and random misfiring. The symptoms may mimic ignition or fuel injection trouble you've encountered on other cars. I cannot address 240 vehicles newer than 87, the friends I help do not own anything newer. In all the 240's I've seen there are several wires that are "flaky": oil pressure; alternator wires and alternator dash signal; knock sensor; water temp gauge; starter from ignition; starter to coil; primary ignition wiring near the ignition coil; and on 7xx cars, harness connectors in the right rear corner of the engine compartment below the ignition coil. ALL the wires from the ECU do not show any signs of deterioration in any of the harnesses we have opened up. Since the flaky set are wrapped into the main harness to replace them means replace everything. At big $$$ for Volvo & the service center. After getting nailed for the 85's harness, I took preventive measures on my 83 and others until we find a long down time to correct the problem. We replaced the alternator and the oil pressure sending wires rerouting them around the right side of the engine bay. We believe that if the alternator wire shorts to some other wire that is where the big problems could occur. The alternator wire has the potential to supply a constant 12+ volts to any of the others ( which are to ground) and act as a heater wire inside the harness, getting hot enough to melt all the others.

In my 85 it was from the starter wire to the alternator wire up by the dash connector and was caught before much damage was done. Had it replaced by the dealer thinking insurance only to find that insurance refuses to cover this problems in Volvo's. Cutting open that harness revealed NO damage or deterioration to any other wires in the harness except the above wires. Our solution: We reroute with new wires to all of the above sensors. Best done with some other time consuming task. To make it really easy we release the intake manifold. Takes two of us about 3 hours to reroute all wires and replace the manifold. Tried it first without releasing the manifold and it took 8 hours. I believe Volvo could have created a replacement harness consisting of just these wires but did not do so because of $$. Another is that if you catch the problem soon enough no other wires will fry because of a short between two of the bad wires. Wait too long and other wires will be damaged from the heat of the short. Since this is probably about the time Volvo found out about the problem, it looked to them like all the wires in the harness are bad. See Dave Barton's extensive discussion of wiring harness woes.

[Quick preventative:] Watch the wires coming from the connector directly under the windshield below the driver and the oil pressure and alternator wires on the right front of the motor. These are the first ones to go. If it starts reroute the alternator wire first as this can cause the most damage if left in the harness. Then replace the starter, then the coil wire as these have the next greatest potential for damage. If you can, get the wires replaced before they cause other damage, do so as the cost will come out of your pocket.

[1983-1987 7xx cars:] If you are referring to the problem of wiring harness rot that affects the 83-87 models, it usually affects the harness on the engine. On the LH cars, this usually includes a fuel injection harness and a separate ignition system harness. However, I have seen some deterioration of other underhood harnesses including the wiring that goes to various lights (turn signals, corner markers, headlights, etc.

[Advice on replacement:] The engine wiring harness went bad on my 1983 240 Turbo (170,000). I noticed it first when my starter would try to engage occasionally when I hit a bump or turned a hard right. The wires up by the firewall on the left side of the car were bare at the connector. I tried to separate and tape them, but that did not work. I found out why when I replaced the harness. The harness runs along the left side of the block, and EACH of the wires was completely bare the majority of the length of the block!! As you know, depending on which ones touched which, anything could happen. REPLACE the whole harness!!!!!! Trying to patch it will only lead you into hours and hours of nightmares both as you attempt to cob it together, and as soon as moisture gets in your cheesy butt connectors and your gauges, idle, starter, etc go wacky!!!

Remember: My Volvo is Turbo. Although a similar process, I can not speak directly on the naturally aspirated version. The job took me (a former diesel mechanic but working with limited tools on this job) 5 hours. I unbolted the intake and pulled it away from the head. Of course to do this you will need an intake gasket. I recommend you do this also, as to work around and under the intake would be treacherous. With the intake pulled away, you can see straight down in there. You may want to replace your flame trap when you are in there as you have a straight shot at it. Any troublesome vacuum lines could easily be swapped out also.

The new Volvo harness is color coded exactly as the original. (big advantage). It is also exactly correct in length. (huge advantage). Just remove the old one, being careful at each connection - temp sensors, alt, oil press, etc. are all very dry. You may have to cut the old harness out in pieces as it is not pliable at all. Install the new one by starting at firewall and working your way along the block and around to the oil press and alternator. It is pretty self explanatory really. Leave about 5 hours to do it. This sounds like a lot, but multiply it times the hourly rate of your local shop, or the cost of burning up a starter (and a tow) like I did, and you will have a little more incentive to clear up some time on Saturday morning. No special tools. (May want torque wrench for intake if you are REALLY particular). I shopped all over and I purchased it from NILS SEFELDT Volvo in Houston Texas (281) 721-1600 (800) 468-0041 for $230.22 and the gasket for $11.70.

[Additional tips from Dick:] My suggestion: do not remove the intake manifold on the 700 series. Remove AMM and hose to intake, idle speed motor and hoses, also flame trap and oil trap. Label stuff carefully. Begin your rewire from under the car, ie the oil pressure sender light, removing the old stuff as you go. Your new harness has yellow bands indicating where the clamps should be. Remove the harness from the AMM and replace with new. You will have to remove the knock sensor wiring and mark it . I think you get the picture. With the oil trap removed, you can clean it and put a new O ring on it (leak source) and new flame trap. Other suggestion is to remove the 3 plug ins on the passenger side and pull then through and under the manifold along with the injector harness stuff.

Believe marking and labeling is extremely important. I blew the brains out of a 240 by mixing up two similar 3-prong connectors. Label the old harness too because you can always compare wire colors in the connectors that are alike.

[More from a VCOA Wiring Clinic, courtesy of the BrickBoard:]

Scope: The problem afflicts 200 and 700 series Volvos manufactured during the period 1983-1987 [Note: several commentators would also include the 1981 & '82 models of 240 series.]. The problem has also appeared in other vehicles manufactured during the same period with Bosch electrical systems. Owners of all vehicles manufactured with Bosch electrical systems during the period should inspect the engine wiring harness. Anyone considering purchase of such a vehicle should inspect the engine wiring harness if the harness is the original.

Presentation of problem: Disintegrating insulation on wires exposed to high temperatures for long periods (10 years or more).

Symptoms: All vehicles within scope are vulnerable to the problem. Close inspection of the engine wiring harness will reveal the problem before it causes short circuits. If a vehicle within scope exhibits drivability problems that are intermittent and cannot be otherwise diagnosed, short circuits in wiring harness caused by deteriorating insulation may be the cause.

Inspection: Use a strong light source and check wiring, paying particular attention to wiring passing close to high heat sources. High heat sources include intake manifold, exhaust manifold, turbocharger, block, firewall.

Common locations presenting problem: B23: firewall near main connector, alternator, intake manifold. B230: ground wires on intake manifold, oil pressure sender, water temperature sensor on block. B28/280: no engines were available for inspection.

Solutions:

Temporary solutions: liquid electrical tape, applied in several coats over several hours, good between -20 and 255 degrees F; shrink-fit insulation, applied with heat gun or torch, good past 400 degrees F, but hard to fit correctly over end connectors; spliced wiring, recommended by some Swedishbricks and SAAB list members as the most nearly permanent fix that does not require a new harness. Standard electrical tape is at best a one-month reprieve. Any solution short of splicing lasts no more than a few months.

[Editor] Normal PVC-insulated wire, used as a replacement, will not last long in high underhood temperatures.

[Tip from Jim Bowers] DO NOT use teflon insulated wire around your car. While it has the best high temperature rating it is notorious for "cold flow". Where it is bent around a corner the insulation will eventually "flow" out of the place where the pressure is and it will short. Kapton is a another high performance insulator that is so good in tests, that it passes the tests with very thin dimensons, saves space and weight. However, over time vibration can wear through the stuff. It has superior mechanical, temperature and radiation properties. "Flex" circuits are often made using it as an insulator. Its "natural" look is orange and semi-transparent. Its so $$$ that it isn't used often. After considering everything, irradiated polyolefin is a good choice.

[Tom Irwin] It may be best to get a good one from a wrecker and graft new sections onto the rot. 1" strip and a union twist in the wire. Silver Solder and a 1,200 degree iron. FLOW it in there. Use a 3M product "self-sealing silicone wrap" used for field repairs on high power lines. Stretch it til it just about tears and wrap your wires tightly. As it heats and ages it melts together and forms a tough, conformal coating. Stuff it in a split loom and tie wrap it up.

Permanent solution: new wiring harness, cost ranges between $250 and $350 (US). VCOA has been successful in persuading Volvo to lower the price of its wiring harnesses for vehicles within scope, and current price range quoted above reflects those reductions. Prices have been cut from 33%-50% from previous levels (Example: old price of engine harness for B230FT engine was approximately $500, now reduced to $270). Dealers who offer club discounts will add their standard discount to the current prices. It is absolutely critical that you order the correct harness. Very difficult to do when there are 3-4 variants out there, yet little way to tell the harnesses/engine applications apart.

Labor Requirements: Owners who prefer to have a mechanic install the new wiring harness can expect to pay 4-6 hours of shop time for the job. Owners who prefer to do the job themselves should set aside one or two days. For the B230 engine, it is recommended that the owner have all vacuum hoses replaced at the same time, as well as fuel injector seals. In addition, performing the job on the B230 engine involves removal of the intake manifold and air intake valve, and so requires replacement of the intake manifold gasket and the air intake valve gasket. Owners who have replaced wiring harnesses of B23 and B280 engines may wish to offer advice on other maintenance that should be performed at the same time, as well as other parts (besides the wiring harness) that may be required. Dielectric grease for multi-pin connectors, as well as an oxidation inhibitor for single connection points to aluminum ground, are recommended. Do not interchange the two, as dielectric grease is an insulator, while oxidation inhibitor is a conductor.

Picture References. Check out http://www.homestead.com/volvo2/harness.html
for visual images and instructions for wiring harness replacement and other maintenance items. See Dave Barton's excellent site for details on the harness problems.

Replacement Procedure:
[Dick Riess] For those feeling threatened by this job, it can be done relatively easily, in my case under 4 hours of puttering slowly. Also, a good source is Dave Barton and his super choice used harnesses.