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Hello, my name is Joe
Is Your motorhome a Ford or Chevy Chassis?
Thanks for the reply,
If your chassis is a 1985 1/2 or newer, there will be an electric booster pump inside the fuel tank. The purpose of the booster pump is to provide enough pressure to eliminate vapor lock between the tank and the mechanical fuel pump.
The electric in-tank pump is powered through a relay, and the relay circuit utilizes an oil pressure switch as a safety shut-off.
Here are the best fuel system and evaporative diagrams I have available.