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I have recently renewed my 12n and 12s plugs on the caravan a 2001 Coachman Amara 500/5

The road lights work perfectly :-  BUT when I try to use the lights in the van when the 12s plug is connected they will not work although the voltmeter shows plenty of power to the van when switched to car

When I disconnect the plug and switch to van no problem and the lights work on the van battery.

It makes me wonder whether or not the battery is being charged when towing and also is the fridge being kept cool (there is no light on the fridge to show it is working or not)

I have checked the wiring in the plug and it is all correct as far as I can see and there are no wires to pins 2 and 5.which according to the van manual is correct.

Am I missing something very basic..

Quote: Originally posted by bordercaz on 29/4/2008

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Pin 4 (green) is the one which charges the battery when the engine is running and diverts to supply a 12v feed to the van's accessories when the engine is not running. It sounds as though there is a problem with the relay controlling the switchover.

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Thanks for that Bordercaz. I now have the answer - According to the firm (SussexTowbars) that fitted my towbar it was around the year 2000 that a relay was fitted in most caravans that prevents you using the car battery for lighting (to stop it from discharging) as most caravans after this time had their own leisure battery. They will, though, still charge the battery and keep the fridge cold when the engine is running.

Seems like I was worring unnecessarily.But you do not know unless you ask.

try www.rydertowing.co.uk

their practical guide to advanced towing electrics shows general instructions for 12s installations with a note about post 1998 vans

Quote  page 40 in italics  ..........that if you wire according to their instructions all caravans will be propelry accommodated

they also give a phone number for advice