My 1998 Yanmar
pressure gauge reads max as soon as I turn on the key and stays there when the engine
is running. I know I have good oil
pressure but there is a problem somewhere in the circuit. When I disconnect the wire to the sender the needle goes to 0. When i install the wire to a replacement sender and ground the sender the gauge reads maximum again. I believe it should read 0 with no oil pressure. What would make the gauge move when power is turned on and then read 0 when the sender is disconnected other than either a faulty gauge or sender? How do I properly test or diagnose the sender unit and gauge?