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Whilst on caravan site at the moment and I  noticed the centre pins to both 12s sockets for the car and caravan had overheated and melted.

I purchased two new sockets and changed 1st the caravan socket for the damaged one - all working OK.

Changed the car socket without disconnecting the car battery, now the connections to the caravan both 12N and 12S plugs are now working at all.  All the exterior lights eg: brake lights, side lights, reversing etc are caput.  Car electrics OK though.

Using a mult- meter and there is current flowing through the plug on the car on some of the inidvidual wiring elements within the socket head Nos 3 & 4.

Have connected two wires direct from the car battery to the caravan 12S plug and systems work OK.

Within the car itself (Rover 75) have checked two in-line fuses on the power lines - OK.

Any help whilst still at the caravan to rectify problem would be most appreciated, as unable to tow the van away.

hope this helps

Trailer Wiring I

Socket and plug wiring instruction
12N Normal Socket		12S Supplementary Socket
1)	Left indicator	1)	Reverse
2)	Fog	2)	Battery Charge **
3)	Earth	3)	Earth
4)	Right indicator	4)	Power feed
5)	Right side light	5)	Spare
6)	Brake	6)	Fridge **
7)	Left side light	7)	Earth for pin 6 (1998 on)
**NB It is essential that pin 6 is wired through a split relay from 1998 on!!

Thank you for your reply.   I have rewired as per the diagrams hence my loss to understand why neither 12N or 12S plugs are not functioning correctly. 

Excellent diagrams, keep them coming as I have problems relating to when the caravan in tow, the fridge won't work and knocks off the internal 12v system. Any suggestions to remedy this would be most helpful also.  Fed up of rotten food when arrive in France for annual hols.

PS:  Where would the split relay be and how can I locate it? 

I would start checking one of the car sockets first with the multimeter to see what is working, and write down the results. Make sure the other is unplugged.

Check each pin in turn, testing between the live pin and its earth return.

If you get a reading then that circuit and its associated earth is OK.

If you get one not working check between the live and the tow bar as an earth. If you get a reading the associated earth is wrong, if no reading the live is wrong.

Work your way through all the pins.

If a live is not working:

• Check the associated car switch is in the correct position eg. if its a side light make sure they are on.
• Check it's fuse on the car
• Check its wired correctly.

If an earth is not working, its probably wired into the wrong teminal.

Then when all is well with that car sockets, plug in the caravan plug into that socket only. Make sure the other one is unplugged. Get that socket and plug working correctly first. Then repeat the lot with the other socket and plug.

Thanks for info Navver

However looking at Michael's diagrame is No 3 the only earth return for all the actions you described to work through?

Car switches are working normally in their own right even connected to the caravan.  It's the caravan exterior lights not working when coupled 12vN plug.

I am a complete novice in electrics you see and help and basic guidance will much appreciated.

Unplug the 12S plug and unhook the caravan so its not touching the car. Then try the 12N. If it works OK the fault is in the 12S.

Yes there is only one earth in the 12N, but there are several in the 12S and each one will be wired seperately to the caavan circuit it is associated with.