Ford Repair: oil light, oil pressure gauge, oil light

Question
The oil light in my 1981 F150 comes on after the engine heats up. The oil and filters have recently been changed and the oil level is full. After driving around for a while after the oil light comes on, there is no knocking.

Answer
your probably loosing pressure due to the motor just getting old.  I would put a fresh filter on, or even use a twin filter kit to increase the pressure.  Run a little thicker oil, maybe 20-50.  Also install a manual oil pressure gauge so you know exactly where your at.