Question

hi tom could you tell me what the white wire is on the 12 volt side on a thetford 145 is having trouble wiring it up if i put it to red wire it blows fuse if i put it to black it blows yet there are only the three wires there it all works on gas and 230 volts confused.

Answer

It could be the D+ wire. This runs the 12v cooling when towing/driving, this should only be live when the engine is running. I could also be the heating element negative wire, are you getting a power reading through this wire?