i had a few ground problems.
The first and badest was the ground on the fenders. cleaning this ports up didn't had any effect, so i changed the wires and this solved a lot of problems.
than the ground cable on the oil pressure sending unit was broken in the connector.
But do you have full oil pressure when you remove the connector from the sending unit?
First do a manual gauge check to be sure you realy have a good oil pressure. Since i've known that my oil pressure is perfect i searched for everything till i found the problem.
But maybe youre oil pressure is realy bad.