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I've been troubleshooting gauge issues on my 1982, in particular the volt meter and the oil pressure gauge. I've studied the circuit board diagram on the Willcox site and watched numerous youtube videos but don't understand how these two gauges get their grounds. If I bench test these gauges they seem to work when I apply ground directly to the ground pins.
In the diagram below, if you look at the volt meter circuit in the lower left, you can trace the ground line that goes between the ground pin on the gauge and three of the dash pod lights, but it doesn't seem to actually get a ground from anywhere. How is this supposed to be grounded?
On the oil pressure gauge in the lower center there are three pins: power, signal, and one that is not connected to anything. In bench testing, this gauge seems to work right when I apply ground to that unused pin. Again, how does this gauge get its ground?
Is the metal gauge pod case supposed to be grounded and these gauges get their grounds from the case? What am I missing?
Circuit boards are all the same 77-82, the only difference is 80-82 has a check engine lamp provision.
If you look at each side of the PCB plug you will see a black wire at pin #9 (left side) and also at pin #1 (right side) both of these are circuit 150 a common chassis ground.
Yes you are correct, When a gauge is grounded by pin #1 or #9 it is also grounding the metal backing of the gauge cluster.
The oil pressure switch pin #7 is the ground for the gauge by resistance.
If your center cluster Instrument lamps are working your getting a ground source.
For example, the clock (Orange wire pin #6) has a single hot wire attached to it, where does the clock get it's ground source...
This diagram I did for my 77, wire colors may be different but circuits are the same except no provision for check engine lamp.
Last edited by bmotojoe; Jan 9, 2022 at 07:45 AM.
Reason: Update to the Update of the PCB drawing
Troubleshooting gauge issues on 1982
