One wire to many?

Paul Osterberg

Today I change the original fresh water pump, with a Jabsco Par Max 4, not a big deal, but to my surprise there was three cables to the old pump, One blue negative one brown positive and a thin black wire also negative. Both the Blue and the thin Black cable was connected to the same terminal on my old pressure switch on the old pump. My question for what purpose does the black wire have?

Paul on S/Y Kerpa SM#259

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