Oil Pressure gauge S terminal - Purple wire from sender
Oil Pressure gauge middle terminal - Black wire (Ground)
Oil Pressure gauge right terminal - Red wire (Ignition-on hot 12v)
The oil pressure sending unit is on the engine block and looks like a small 2 X 3 inch filter with one terminal. There may be another sender plumbed in the same area that has two connectors. It is an oil pressure switch that is supposed to close below 4 psi to activate a dash warning light in some speedometer clusters.
To be sure the problem is not the gauge, you can momentarily short the wire from the output of the Sender to ground. If there is no resistance, your gauge should read 80 psi. DO NOT hold it for long in this position. If the needle does not move from zero psi then, either the wiring (open circuit) or the gauge is bad. If it does move, the sender unit is bad.
It is very common for the sending units used with the 258 and 232 engines to be inaccurate. Make sure you have a good connection to the sending unit.
It is easiest to test the sending unit by temporarily plumbing in a good mechanical gauge.
Pressure (PSI) Resistance (ohms)
Jeep CJ Gauge & Sender Diagnostics
by John Foutz
[img]/wwwthreads_images/icons/crazy.gif[/img]<font color=purple> It's a JEEP thing!</font color=purple> <font color=red>1985 CJ7 </font color=red>[img]/wwwthreads_images/icons/crazy.gif[/img]