I always leave both switches set on. When on campsite hook up, the green light is on. When hooked up to the car, with engine running, the red light is on. Linz checks as part of the road light etc. check prior to setting off.
The OPs prob is that the red light doesn't come on when hooked up to the car, with the engine running.
His car electrics are fine. I know because I checked them!

Ian

Surprised no one has suggested that the 12v element may need replacing? my 230v one failed last year and needed to be replaced by my service engineer.

On the new fridges there are no lights, just a round dial to set to 12v / 230v / gas, but there is an interior light, if that lights does it mean its working?.
Dave

Looks way beyond my IQ

Dave, I don't think the internal light guarantees that the fridge is working. It operates whether the fridge is on 12v or 240v which suggests that it has its own separate supply.

Thanks to Addick 100,(Ian), for checking my electrics and for other sage advice.
Before leaving our campsite I checked the fridge with the engine running and the red light was on (?!?). A self healing Troll perhaps. Hopefully it will now continue to function properly. Thanks for all the suggestions.

Julie, As stated earlier the red switch is for when you are towing provided you have the 13 pin arrangement or the 6 & 7 plugs arrangement. To use it you should switch the green to off (down) and switch red to on (up) . To test start the car and rev it slightly and the red switch should illuminate. It could be that if it does not illuminate, the switch itself is faulty.

As it's such a glorious day I decided to spend it next to the car exhaust in an attempt to figure out if my fridge works on 12v or not.

Found an article on checking tow bar electrics, got the multimeter out and can at least confirm that the car's ok. Get a +ve voltage on pin 10 when engine is idling.

Connected to Troll, switched 12v switch on, engine idling, no light. Got Nia to sit in the car and hold at 2000rpm, waited 5 minutes, still no red light. Was about to give up but opened the freezer compartment and element felt cold and there was condensation forming. So it looks as if I may just have a blown bulb in the switch.

However, decided to repeat experiment with thermometer just to be sure. Left fridge and freezer door open to allow them to get to room temp, placed thermometer in freezer compartment and repeated what I'd done earlier. But nothing happened. Didn't appear to cool at all. It had got a fair bit warmer by this time and if I'd have continued for longer than 5 minutes it may well have worked.

I at least know the car electrics work now but I'm still not 100% sure if the fridge works or not. What I intend to do next is not precool the fridge when we next go away and see if it has cooled when we get to the destination.

Quote: eribanaut wrote in post #19

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On the new fridges there are no lights, just a round dial to set to 12v / 230v / gas, but there is an interior light, if that lights does it mean its working?.

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Hmm! That switch is set to on on my bip. I'd no idea what it controlled so I left it as it was. I wonder if I set it to off whether the 12v to fridge would work. If it does what you say it does it implies that it switches the supply from pin 10 as there should be nothing on that when engine switched off.
Could also explain why I felt that fridge had worked for a bit as engine was turned off for a while whilst I tried to figure out what to do.
I'll try it when I get home from work tomorrow night.

I have often wondered if mine works on 12v as rather like testing the brake lights I find I cant be in the car and somewhere else watching at the same time

I always start up the car do light checks, and pop my head in the door to see if the 12v light is on the fridge, set temp and then lock up the door before heading off.