Check Engine Light

I have a 1989 Chevy Silverado.(350, automatic trans) When it is started up the oil pressure gauge shows about 15 pounds. After the engine gets warm the gauge pressure drops to next to nothing (1 or 2 pounds). The engine runs fine and has plenty of oil. Could the problem be the oil pressure sending unit? If so, where is it and how is it replaced? If not the sending unit, what else could it be?

15 pounds sounds a little low. My engine has 250,00 miles on it and has 40 lbs at idle. I would try changing the oil, using the correct viscosity. If htis does not fix the problem, it is possible for the pressure relief valve to be stuck open, causing a bypass condition. Not knowing the mileage and condition of the engine, it is difficult to know. Does the engine make noise? Internal engine wear, such as worn bearings, on either rhe crankshaft or the cam bearings could cteate this condition. The location of the sender is either on the oil filter pedestal or the area directly below the distributor. If you have a gauge, (apparently so,) you will need to replace it with one calibrated for the same gauge as yours. Ray

First step put a test gague on it, to verify its not a gague/sending unit or wiring problem. If the mechanicle gague reads the same, start getting some prices on a motor! Hope its just a failed sender.