Caravan electrics

[Mr-H]

When my caravan is unhitched from the car the 12volt dial inside the van reads 14 volts. However, connect the car and the dial reverts to zero. I'm sure this is not correct. Indeed, there is no 12volt power in the 'van if the car is connected. I have checked the fuses in the 'van, and cleaned the plugs and sockets which provide the connection at the back of the car. Is it thje charger where the problem is? When hooked to the mais elect the dial is back to 14 volts rate of charge. Where do I look now?

[AlBags]

So I presume you are using a Zig box in the van (Power centre for car 12v and on-site mains charging and distribution)?
Are you using a supplementary 12S socket on the car (properly wired) as well as the standard 12N, or have you the newer compact multi-pin socket)?
Sounds like the car feed 12v is not getting to van. Start the car and check again. There is probably a split-charge relay in the car that only allows power when car alternator is charging. You need to check that first. You may have both auxilary 12v and also Fridge power, both from the car.

[Mr-H]

Connection is by the old 12 N and S plug/socket. One thing I have not done is to check that all of the pins are are live. I suppose that the 12v supply feed from the car could be corrupt at the socket?

[AlBags]

TBH, most problems with caravan functions are poor earth from the 12N.
Check what lives you should have at 12N and 12S (probably 2 on this one, one maybe only with engine running) and what lives there actually are.