1979 Canadian bj40 with Aussie 3B. 24 volt rig. Oil pressure shows zero at all rpm’s. Grounded the wire connection to the sender and gauge went to max. Removed wire it went back to zero. Old sender was stamped 12V. Bought new sender and installed on totally dry stem to assure good ground. Still no reading. Engine sounds good so I I think it is getting oil circulation. Out of ideas. Need help please.