I just bought an '88 F150 4x4 yesterday, and I've noticed that all of the gauges seem to be way off. The oil pressure gauge needle is way to the left of the "L" mark (I know it has good oil pressure because the previous owner installed an aftermarket gauge that reads fine), the fuel gauge went from bouncing between 1/4 and 1/2 tank before I filled it to being well past the F mark after I put another 7-8 gallons in the tank, and the temp gauge is just past the H when it's in normal running temperature range. I'm not sure if the speedometer is off or not, but it seems like it reads faster than I'm actually going. I read something about an instrument voltage regulator causing similar problems, but that was for a newer pickup than mine and they didn't mention which years of F150 had an IVR. I've also read that the fuel gauge is sometimes off if the battery gets disconnected when the tank is less than 1/4 full.