All Ford trucks '87-up DO have a pressure "switch" from the factory. Not a sender. '87-96 have a resistor on the back of the instrument cluster that causes the gauge to go to mid-scale any time the pressure is over 6 psi
. '97-up have no resistor - the gauge itself is built to show mid-scale when the signal terminal is shorted to ground.
Regardless of switch or sender, the 4.9L block's oil pressure port is where mrainey described: #9 below.
The captions of these pics describe how to convert from the newer switch to the older sender. For a straight 6, you don't need the plumbing - just the sender & the jumper wire.
You might also be interested in adding a LOW FUEL light