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I noticed that my grey 12S socket on my towcar had melted around the centre pin so I decided to change it. When I tested the old socket my reader told me that pins 2, 3 and 6 were live. I bought a new socket and connected it up as the original one was, carefully replacing each wire one by one. I then noticed on the instructions that pins 2, 4 and 6 should be live i.e. pin2 for battery charging, pin4 for power supply and pin6 for fridge.

It appears that pins 3 (earth return for pin 2 and 4) and Pin 4 are wired incorrectly (and always have been) but if this was the case, what should not have worked on the caravan when it was connected to the car?

may help

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!!

Have a read of this http://www.towitall.co.uk/faq/faq1.htm

atb

Wizard

Thanks, so if pin3 and pin4 are connected up incorrectly i.e. pin3 to green and pin4 to white, should anything happen when I plug the caravan to the car?

Quote: Originally posted by Mr Jones on 15/7/2010

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Thanks, so if pin3 and pin4 are connected up incorrectly i.e. pin3 to green and pin4 to white, should anything happen when I plug the caravan to the car?

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I would think you'd blow a fuse somewhere as the car would be supplying live into earth cable on the caravan . Either that or things that should work in the caravan when towing wouldn't work .

atb

Wizard