Jennifer has the answer . Your split relay cuts out the charge to the fridge automatically when the battery needs more current from your alternator , this is to prevent flat car batteries . Tickover may not provide enough power from your alternator for both batteries and fridge . You could also be suffering voltage drop caused by too thin a wire from the car battery through the relay to the fridge . You can increase the thickness to 4mm or double up on your existing wire .
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