my 95 f150 has 200000+ miles on her . my oil pressure is for the most part in normal range , however it will sweep from normal to zero while sitting at a red light .oil level is good. what can it be ?

 

Unfortunately these gauges are basically just idiot lights. Sometime in the late 80's ford went from a variable sensor to a switch that turns on at 8 pounds and put a resistor across some of the wiring in the instrument cluster. The net effect is that if the pressure is below 8lbs, the gauge drops to nothing, the instant it goes over 8lbs, it goes to about the middle of the gauge. I think it took the idiot factor out, too many people were going back to dealers and asking why the gauge moved around so much (It's supposed to, idiot...)

Sounds like you're running around 8lbs, not good at all. I'd get a real oil pressure reading with a real gauge, you might need a rebuild or service.

There is also a minor modification you can do to get an actual variable pressure stock gauge by putting a sensor for an older truck (larger) in place of the switch sensor and soldering a straight wire across the resistor on the back of the instrument cluster. I think there's a tech article on here about it. I did it and it worked great. About $15.oo, IIRC. Of course it's still not accurate but at least you can see it move and get a better idea of what's going on. It's easy to add an aftermarket gauge too. Just get a "T" with 1/4" pipe threads at the local hardware store to run both.