I have always been under the impression 80-86 has real "gauges" with proper sending units but not calibrated to the gauge face hence no numbers, while '87 and up has on/off switches which display on gauges. In this regard the oil pressure on the 4 80-86 trucks I've owned always correlated with actual engine conditions and mechanical gauge on the trucks I've had a proper gauge on. i.e. cold idle gauge reads higher, hot idle lower, 2000-3000 RPM it reads much higher than at idle all the while corresponding psi on the proper gauge would be about 70, 25, 50 on a tight engine with HV pump or less on a worn factory engine. Range of motion generally NO hot idle, RM at higher RPM. Yes the gauge is a bit slow to respond, but certainly a lot more useful than an on/off switch at whatever psi.
Similarly the temp gauge you can watch as the engine warms up and the readings at a given temp on the factory gauge always match the aftermarket gauge. With the IDI it always comes off cold advance/high idle at the same spot on the gauge. Operating temp is always in the same area. I will say with the Ford sender on teh IDI operating temp 180-190 was I believe around R which is where the 3 other 80-86 trucks I've owned have always been at 180-190. That sender failed and after replacing with aftermarket 180-190 is around AL, kind of freaked me out at first because I only ever seen these trucks around OR range at normal temp.
Regardless, a functional gauge that gives relative readings is a lot more useful than an on/off switch regardless of if it's hooked to a light or a gauge. I can't speak for '87 and up Fords as I've never owned anything newer than 86. If OP... Blah nevermind, I saw 85 and 84 in the OP's sig and thought that's what he was talking about. If it was an earlier truck I'd say it indicated a problem, on a '94 probably not but throw a mechanical gauge on it either way to be sure. Even the early gauges can read low if you have a loose/dirty connection or any low voltage condition.
