Blue Truck Parts

  The Ford truck line fro 1987 to 1991, which includes F150, F250, F350 and Bronco's, used a full set of gauges that included oil pressure and voltage gauges.  Unfortunately half way through the production run Ford hobbled the oil pressure gauge turning it into a glorified indicator light.  Sensor vs Switch Typical Oil Pressure Sensor The 1987 to 1988 trucks included a fully functional oil pressure gauge.  They used an engine mounted oil pressure sensor that sends a variable resistance signal to drive the gauge.  The sensor is grounded to the engine block.  When oil pressure is low the signal wire will show roughly 100 plus ohms to ground which causes the gauge needle read low.  The resistance drops as the oil pressure increases.  Under normal operating conditions the sender will show roughly 20 ohms causing the gauge to read a little over half way.  It's not a precise system, but it works. Typical Oil Pressure Switch Starting in 1989 Ford replaced the oil pressure sensor with