Tow bar 7 pin S electrics

[Caravannut]

I have encountered an issue whereby when the 7 pin N and S connectors are attached from car to caravan it blows the fuses to the motor movers and the interior lights. Also it shows the reversing light on all the time.
I then attached a different car and the reversing light was only on when car put into reverse. Any ideas?

 

[Jules_ht]

Does the same car blow fuses on other vans?

If you've swapped cars and the caravan behaves OK, then it does imply it's the car. Does it have factory, aftermarket dedicated, or generic trailer wiring?

You can buy trailer light testers from eBay for next to nothing, might be worth popping one on and seeing if any wires that are not supposed to be live are live, which might give some guidance as to where the problem is.

 

[Woodentop]

I have encountered an issue whereby when the 7 pin N and S connectors are attached from car to caravan it blows the fuses to the motor movers and the interior lights. Also it shows the reversing light on all the time.
I then attached a different car and the reversing light was only on when car put into reverse. Any ideas?

This suggests a wiring error. The connections are:-
1 Rev light yellow
3 Ground white
4 Positive supply green
6 Fridge red
7 Fridge earth black

3 and 7 may come from the same point in the car but they are separate in the caravan. Make sure they have a good bond to a solid connection - better still run a thick cable (6mm or 10mm flex) back to the battery earth. These two pins are notorious for overheating allowing the pin to move in the socket mount and cause short circuits to other pins. If you don't use pins 2 or 5 they can also be paralleled up for better earthing.

4 is permanently live. It replaces the caravan battery supply when connected for towing.

6 is only live when the car engine is running. When it activates (to supply the fridge) it also operates a relay in the caravan that disconnects all 12V from the caravan internals but makes a connection to the caravan battery to charge it. By definition (given the fridge can pull typically 120W) the cable feeding pins 6 and 4 should also be fairly large - 6mm minimum.

One question that needs an answer: does it need both 12N and 12S to be connected for the mover fuses to blow or does it also happen when only 12S is connected? If the former (both) then you have an even more complicated wiring fault.

 

[glenno]

If it worked fine before and has only just started happening the most likely cause is a loose wire in the car socket touching another wire. Open up the socket and check.

 

[chrisn7]

Does the same car blow fuses on other vans?
You can buy trailer light testers from eBay for next to nothing, might be worth popping one on and seeing if any wires that are not supposed to be live are live, which might give some guidance as to where the problem is.

I would agree with this suggestion, as you then have the tester in the car to address any problems when away from home for example. This will tell you immediately if the problem is the car or the van, so you are the already half way there! If the sockets/plugs are getting on a bit, water ingress is a real possibility with corrosion of the terminals and wires.