Originally Posted by marc abrams

First you need to establish a baseline to what kind of amperage flows through these sending units because I have no idea. You have two other gauges that work, temperature and fuel gauge. So let's use them. Disconnect both the temperature and fuel sending units. With a ampmeter in series from ground to the sending unit wire measure the amperage. Then do the same with the oil sender. I'm going to guess you are going to see a higher amperage on the oil pressure circuit cause by the oil pressure gauge itself. So you don't fry another oil sending unit, try installing a inline fuse on the oil sending unit until you find the problem. And besure that you have the correct fuse in the gauge circuit before you start testing.