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Fixing oil pressure gauge

zzb3886

Member
Joined
July 20, 2008
Messages
16
Reaction score
0
City, State
Seattle, WA
Year, Model & Trim Level
00 XLT SOHC
A month ago, I suddenly realized the oil pressure gauge on the dash board showed zero oil pressure. I was on the freeway when I panicked and pulled over from the nearest exit.

It turned out to be a wrong reading as I drove a few miles home after checking the engine on the side of the street. As many posts suggest, I replaced the oil pressure switch and hoped that would fix the problem. But it didn't. I then measured the resistance of the switch after turning on the engine, and the switch was connected. This indicates a wiring or gauge problem.

Later I measured the resistance of the oil pressure switch connector to the ground, with the oil pressure switch unplugged. It showed several hundred ohms. This means the wire from the connector to the dashboard is good, otherwise the resistance should be infinity. Because the only connection between the wire to the ground is inside the dash board. I believe the problem is in the instrument cluster.

Today I finally got some time to take the instrument cluster off. I followed the instructions in http://www.explorerforum.com/forums/showthread.php?t=46290&highlight=indiglo+install. As a reminder, be sure to disconnect the battery terminals and wait at least 2 minutes before doing this.

In the back view of the instrument cluster, the oil pressure gauge is on the top left. There are three terminals, marked as "B", "S", "G". (I think they represent "Battery", "Switch", and "Ground", respectively) Normally, the "B" terminal is connected to +12V, the "S" terminal is connected to the oil pressure switch, the "G" terminal is connected to the ground. When the oil pressure is (very) low, the switch is open, the gauge shows a low reading, when the oil pressure is normal, the switch is closed, the gauge shows a high reading.
back.jpeg


Measuring from these three terminals, everything is connected. But this doesn't mean the gauge is good, because the "B" and "G" terminals are shared and connected through many circuits. I had to take the gauge off completely, after gently prying off the oil pressure pointer and the right part of the instrument cluster panel. Then I found a broken thin wire near a terminal (shown in the red circle).
broken.jpeg


I took one turn off the coil to get some longer wire. It doesn't matter since there are still hundreds or thousands of turns in the coil. Then I soldered it back to the terminal.
prepare.jpeg


The pointer position has to be calibrated again. To do that, as well as for testing the gauge, I hook it up to a computer power supply. The "B" terminal is connected to +12V, the "G" and "S" terminals are connected together (simulating full oil pressure during running) and connected to the ground.
testing1.jpeg

testing2.jpeg


Double check the wiring because the computer power supply is powerful enough to fry the gauge! After the power was turned on, I pushed the pointer back onto the gauge. It doesn't need to be very precise as it's, you know, an idiot gauge.
testing3.jpeg
 
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