Volvo Towbar Electrics - Post 1999 Caravans

That wonderful thirteen pin plug!

I have been fortunate in being able to obtain for myself a new Volvo and being a caravanner I naturally asked for it to be fitted with a tow bar. As I wanted it to be very neat and tidy I decided to go for the removable towball and, reluctantly, the thirteen pin plug that the German motor industry has forced on the world of caravanning.

Now anyone who has towed a caravan will know about the two seven pin connections between the car and the caravan. One called a 12N is black, has seven pins on the plug that locate in a seven pin socket on the back of the car. Assuming the car has been correctly wired up in the first place thes the 12S connects the reversing lights on the car to the caravan, (assuming the caravan has reversing lights!) and also connects up the fridge in the caravan, the interior 12 volt lighting and also charges the caravans interior 12 volt battery.

Now until 1998 all was well with the caravanners world the above system was understood by the vast majority of people and cars and caravans worked in unison to provide their owners with a comfortable existence.

Then in 1999 the first fly arrived in the ointment someone suggested quite sensibly as it happens that as the fridge used a lot of power it should have its own return (earth/ground) cable as well as supply. The wiring was suitably altered and as long as everyone new that the caravan was wired to the new standard all was well.

Then along comes another fly, our German friends and their new plug. Much tidier, secure (it secures with a bayonet catch) and less hassle when bending down in the rain hitching up the ‘van. BUT the thirteen pin plug cable is thinner and won’t really safely run a fridge. It gets too hot. So to run a fridge you need the thicker cable fitted in the 12S socket.

Now to satisfy this need and also to help those of us with British caravans fitted with 12N and 12S plugs our friends in Germany make an adaptor which connects the German thirteen pin plug to our two British ones and this is the one that Volvo supply you with when you ask for one.

Now if your caravan is pre 1998 it will run everything but the fridge (I think) as that pin in the seven pin plug is not connected. But if your van is 1999 on, and ours is 2000, it won’t! Someone forgot to tell Volvo so they only supply the one plug adaptor. It took me a weekend and a Monday to sort the problem out. Two Volvo dealers, Brink the towbar people, the Caravan Club, Towsure and my local caravan dealer were not able to answer the problem, so in desperation I took the 12S plug apart. I then sat there with my multi meter and the adaptor and slowly worked through it and in the end sorted it then reconnected it as below.

The pins numbered 1 to 7 in the thirteen plug connect in numerical order to pins 1 to 7 on the 12N bit pins 8 to 13 do not run numerically in the 12S, the following applies for a post 1999 caravan.

13 Pin Plug		7 Pin Plug
Pin 8	connects to:	Pin 1 (Reversing light)
Pin 9	connects to:	Pin 4 (Constant 12v power supply)
Pin10	connects to:	Pin 6 (Fridge power supply)
Pin 11	connects to:	Pin 7 (Fridge earth)
Pin 13	connects to:	Pin 3 (Earth line for pins 1 and 4)

So if you have a thirteen pin plug and a post 1999 caravan using a Volvo (manufactured by Volta) supplied adaptor then although your road lights work other things may not, so off you go you know you won’t rest until you find out, back the car up to the caravan and see what is actually working. You might be surprised.

Just one more thing, when my V70 was wired up by the technician,in the towbar wiring harness, which the manufacturer in their wisdom wire up using only white cable with numbers printed on the ends, cable 11(from pin 11) should be connected to earth. Mine was cut off!! It was considered redundant! I made it good again and ran a suitably thick cable to a good earth point.

I do hope this makes sense when you read it, it took me some time to ‘sus’ it out.

Dennis LeWorthy

And as a postscript I have just found that Towsure also market an adaptor and from looking at the catalogue picture it appears that they use a 12S and a 12N cable into the thirteen pin socket so maybe theirs works everything. I shall have to investigate Lastly the Towsure one is only about £24 which is a bit, quite a bit, cheaper than Volvos.

Important: Read also THIS DOCUMENT from the Carvan Club.

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