Thetford N109 12v connections

[Becca143]

Hi,

We are converting an old ambulance to a camper and have an unused Thetford N109 fridge. Trouble is, we can't work out the 12v wiring!

240v is working and the gas is working. We have a group of 4 wires, 2 thick (red and white) 2 thin (black and purple). Can anyone help with how these should be wired please? Any help hugely appreciated!

 

[autorouter]

You probably know this already, but just in case you don't - there are two separate 12V supplies to a 3-way fridge.

The High Current (HC) goes to the 12V heater element, usually from the starter battery via a fuse (20A) and a relay that switches on when the engine is running. Power comes from the alternator, and cuts off when the engine stops to avoid flattening the starter battery. They will be the two thick wires, but check the polarity, don't guess.

The Low Current (LC) goes to the fridge control board and the gas igniter etc. It is permanently on, connected to the leisure battery. Again check the polarity, don't guess.

 

[Becca143]

Thanks for that info the issue we have is that the fridge has the LC and HC marked on the terminals but not +&- is there any way of testing or do you know which terminal is +&- thanks for your help