First lets ck your sender to see if still works...
The output screw at the bottom is isolated from the Body of the sender... The sender is a variable resister the varies with the pressure input. So..... just sitting there with engine off and cold measure from RESISTANCE from the Threads on Bottom to the body or the threads where it attaches to block.
That is a 0 , zero, pressure reading.... That one is easy... should be 68 to 70 range or so.
Getting at at pressure reading/ reistance off the sender is a bit more tricky. The sender can be pressurized by air and a regulator and some brass pieces.... The sender threads is 1/8 NPT pipe threads and hardware or big box stores like lowes, menards, etc have the brass parts for 1-2$ each pc. Can also use a 1/8 NPT brass pipe and T or Manifold and mount the sender and a Mech Gauge on the engine... On start up cold, max press see what the gague pressure on engine and the reistance of the sender... write it down... Should match what is below or close.... if close then it is working...
I think the gauge gets ground from the dash..... So you will need to ground the gague to get it to read...... If I rememeber this right....
Info from past write up....
The old Jeep Sender and Gauge parts and information is messed up at this time. I went thru this about a year ago, there is a general mixed up of the SENDER resistance ranges and the OEM electric gauges that will work correctly with them. So I dug in to fix my issue and this is what I found on the resistance ranges of stock CJ gauges and senders……….. this what is being sold new and what will work for our CJ..
The older CJ's of the 70's use a 2" thick gauge and their own Specific sender and resistance range.
The newer 80’s Cj's have a 1" gauge and a different sender and resistance range.
Full Size Jeeps for the 70s & 80s… also called the FSJ, for these same years have yet another gauge and sender combo with another resistance range. The Field Service Manuals have the resistance levels / ranges listed for the jeeps years of interest if you need to ck the numbers further…
Some time in the 1980's Jeep CJ went to a 1" thick gauge and the oil sender resistance ranges are different. Crown does have a sender that will work, Crown #3212004 and sells for about $20. Morris 4x4.com was selling at 10% discount for a forum discount at the time so it cost me $19 and $4 to ship. Morris and Crown at that time list this for 1975 to 1986 for all CJ, Wagoneers and THIS IS NOT TRUE. THE CROWN SENDER WILL ONLY WORK WITH THE CJ NARROW 1" GAUGE.
This is what I measured with the Crown sender and a pressure regulator, gauge, and multi meter.
Pressure............Measured............spec range
0-3 psi..... ..........70 ohms...........68-70 ohms
20........................33......................
40........................23..................21-25
60........................14....................
80.........................9....................7-13
the FSM covers much of this in the gauge section
