So it's working as it should on van but the switch is the opposite if what it should be. But it does work.
When the switch is on van do all the internal lights and pump etc work.
1. When connected to car and engine running. They should not.
2. When connected to car with engine not running. They should work from car battery. Prove by disconnecting van battery.
3. If not connected to car. They should work from van battery.
If all this is as I said it should be safe to tow like it.
As I understand it, the car van switch was before habitation relays were used. Nowadays its all automatic with the habitation relay doing all the switching. It is voltage operated so knows if the engine is running and knows whether its connected to the car or not.
Basically it should be as follows.
12s plugged into car and engine running. No internal 12volt works but fridge works and battery charges.
12s plugged into car and engine not running. Internal 12volt works from car battery and fridge does not work except on gas and battery doesn't charge.
Not plugged into car and no EHU. Internal 12volt works from van battery and fridge does not work except on gas and battery doesn't charge.
Not plugged into car and EHU plugged in. Internal 12volt works from van battery and fridge does not work except on gas or 240volt and battery charges.
The reason the internal electrics should not work when the engine is running is to ensure that faults with the internal van wiring do not in any way affect or prevent the car or trailer lights and stop lights and indicators etc electrics working correctly.
Yes a very well written explanation Navver. Answers as below:-
1. Correct, no 12v with engine running.
2. When I disconnect van battery, there is no 12v in van at all with car connected (either with ignition on or not and switch set to car or van).
3. Correct they do.
Hope this makes sense to you more than it does to me!!
Thanks again. Gary
Thanks Navver and all others for your great help and advice. I will be recommending this forum to all I can as it has been quite friendly and you all seem so knowledgeable.
Many thanks once again and happy caravanning!!!