RV Fridge with No Temperature Controls

Now there's a new problem. I have 12V wires meant for my old three-way fridge. When I insert them onto my new 2-way fridge and turn it on and press the auto button which should make the fridge work on 110V it begins to make a clicking noise and it doesn't go away. HOWEVER when i take some wires and connect them directly to my battery and then to the fridge it works just fine. I would just leave it hooked up directly to the battery but the wires would have to be sitting next to propane line and city water connection and be passing through a storage unit on their way from the fridge to the battery. It seems pretty unsafe. I just cant understand why my 12V wires meant for the fridge make it behave that way.