Instrument Voltage Regulator and Gauges

I am hoping someone can point me in a direction to resolve an issue I am having with my Fuel and Temp gauges. I have been assembling my ‘67 GT Standard over the last 10 years and the car now runs and drives and is basically complete with the exception of three or four issues. Two of these issues are the Fuel and Temp gauges not working.

When I put the car together, I installed the new electronic IVR. Because the gauges were not working, I hooked up my gauge tester from Desert Classic Parts and it indicated the IVR was not working. I then tested the voltage coming into the IVR and it showed 12.4 volts with the key in the run or ACC mode. The voltage coming out of the IVR was 4.9 volts. That made sense to me. I also tested the voltage at the end of the wire coming from the IVR output terminal that feeds both the Fuel and Temp gauges. That showed 4.9 volts - which also made sense to me. However, when I connect the wire from the IVR output post to the posts on the gauges and then test the voltage on the exposed portion of the gauge posts it shows -0- volts. Similarly, if I connect the gauges to the IVR output wire and then test the voltage at the IVR output terminal - it also shows -0-. But, if I disconnect the IVR output wires on the gauges - the voltage on the IVR output terminal returns to 12.4 volts. I do not know enough to be sure if this is a problem or even how to rectify it if it is a problem.

I happen to have an extra new electronic IVR - so I switched the IVR’s - same result. On the off chance my gauge tester was not working properly, I tested it on my ‘69 XR7 and it worked as it should. I also confirmed I was connecting the IVR output post to the correct gauge posts. Although it is entirely possible I have done something else stupid.

While I can - and I am - driving the car, I would really feel more comfortable if I could get the Fuel and Temp gauges working. If anybody has any suggestions as to where to look next, I would really appreciate any ideas.


My bet is that either gauge is mis-aligned in the dash cluster such that one of the posts is touching the metal housing. When that happens, the gauge becomes grounded and you’ll now read 0.0V. Since both gauges are connected via the IVR output wire, one gauge will affect the other.

Disconnect that wire and measure resistance from post to chassis. If you see approx. 0-1 ohm, that post is grounded. If you see 14 or so ohms, then the other post is grounded. Re-seat the gauge in the cluster and re-test.

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Thank you so much. I will check it out. I really appreciate your help.

Similar malady on my '70 base, but without the testing; I could have other issues. I do appreciate the diagnostic advice and will make sure I incorporate that when I FINALLY get around to gauges. I can’t imagine what it will be like not to have to calculate my mileage to determine if I have enough gas to make it to the convenience store!

I’ve seen similar issues when the wiring harness is not fully seated in the instrument cluster.

I recommend double checking that the connector is inserted completely, top / bottom, left / right ends fully seated.

No voltage at output of gauge means it’s grounded

Thanks to all for your suggestions. Midlife and xr7g428 were exactly correct. As Midlife suspected, both gauge posts were not centered in their respective openings and were resting on the chassis. I centered them up and the gauges now test perfectly! I will reassemble, drive and see if the gauges work - and if they don’t - I will know it is a sending unit issue.

Thanks again - I really appreciate the help.

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That means I’m now 1 of 4734 tries at being correct (according to the ex, of course…)

I thought I was WRONG once; turns out I was mistaken.


If a man speaks, and there’s no woman there to hear him, is he still wrong?

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