I put a new oil pressure guage in my '88 F-150 with the 300 6 cylinder engine. Started the engine and the guage never moved. So I put a new genuine Ford sending unit in the engine block. Started the engine and the guage slowly went over past the line to the high side. Now the guage doesn't move from that high reading even with the engine off and ignition switch turned on.

The reason I changed he guage in the first place, because the old guage just sat at about 3/4 of the way toward high. It was that way for years, I never had a working oil pressure guage. Also that red engine light doesn't come on when the ignition switch is turned to on, don't remember it ever working. I changed the bulb even though it looked good when I replaced the oil pressure(integral with the gas) guage. Any ideas what's wrong?

 

The oil pressure sending unit is not an analog sensor. Instead, it is a pressure switch. On the back side of the instrument cluster, there is a resistor that sets the point where the needle sits in the gauge when the power is on. The needle will only move from that point when the pressure sending unit (switch) opens and the needle should go to zero meaning loss of oil pressure.

If you search, there are write ups detailing how to turn the dummy gauge into a functional gauge by installing an analog pressure sending unit (I think from the pre 1980 trucks) and removing the resistor from the cluster to allow a normal analog sweep.

 

Thanks for the reply DIYiT. I'm not interested in turning the guage into a real guage. Do you know what it would take to get the guage working as designed and the red engine light working? I'm pretty sure the two not working are related. Would I need to replace that resistor you mentioned?

 

I think '88 was the last year for the variable resistance sender. It sounds like a switch was installed instead, causing the gauge to swing past high. There's a possibility that the gauge was damaged if this was the case.