No Oil Pressure

bob_o said
The Oil Pressure gauge is mechanical. Sending unit for the dummy light is the one from the truck.

That's my point- trucks usually had factory gauges, cars generally used lights; and the senders are not interchangeable.
Factory light sender:

Factory gauge sender:

Neither will work in the incorrect application.

cudamark said
Sure you put oil back in it? :lol: Also, use a live gauge to check the oil to eliminate the factory sender and gauge/light.

Along the same lines:
Did you change the dipstick and tube when you changed the oil pan? The truck dipstick is the completely wrong length for the car pan, and you could have a seriously low oil level if you filled it according to the wrong dipstick. Just sayin'.