Well it looks to me like I have a mechanical oil gauge. Tube travels from a combined oil filter hose/oil gauge tube fitting at the base of the engine to the oil gauge. Don't have a "master gauge" and a quick call says flaps don't carry them either - kinda laughed at me "old school" he said, "try Snap On". Must be a specialty tool? Unless I'm missing something (entirely possible) and that oil gauge is still somehow electrical (it does seem electrical would be the only way the reading would differ od to not od, as you said). So I will start checking ground wires again. Have had that trouble in the past. Thanks for the help! Dale