Now when I turn the key on, both the fuel and temp gauges peg all the way. OUCH that’s not right.
Any suggestions, please
I’m going to guess you have a 69 or 70 dash cluster. If so, your problem is that one or both of those gauges are mis-aligned in the dash cluster and one of the two posts is touching the metal housing where the posts exit through the small rectangular cut-out. Cheapest solution is to line each cut-out hole with black electrical tape.
Or the ground on the instrument voltage regulator is lifted and not grounding. Do not leave the gauges pegged as they will fail
This will also happen if the IVR has failed. Whether the IVR has failed or isn’t grounded the result is full battery power to the gauges and they will burn out fairly quickly.
No screws securing the gauge cluster to the dash will do the same thing.
You guys are great, but let me give you more information. I have a 68, I took the dash off due to a paint change. While to dash was off, I replaced all lights with LED. Replaced the dash and when I first plugged it in, turned the key on, both gauges slowly pegged. I took the dash off and noticed I did not tighten the four screws on the gauges. ( I need to loosen the gauges to remove the blue filter) Now when I connect the dash I get no activity from both gauges. I am manually grounding the dash so I know it’s grounded. I also have a one-wire alternator, so I think the voltage regulator was removed. - I think. Everything else on the dash works except the two gauges. Oh, and the white lights look great. What is the IVR?
Instrument Voltage Regulator.
OK Royce, that makes sense IVR. I know exactly where it is. Question, is there a way to bench test it or should I just get one that I saw on WCC, part number 10859. Also, does the IVR service both gauges?
The reproductions work terrible - don’t waste your money. The factory shop manual tells you how to test one. It serves the fuel gage and the temp gage and oil pressure on the XR-7.
With the harness unplugged from the gauges you need to verify that ther is NOT continuity from any gauge post to the metal around them.
The IVR puts out pulses of 12 volts. Averaged over time it is equal to 5 volts continuous power. Only very expensive multi meters have the very long integration time base needed to average the pulses. What you can do is use a test light to verify that you are getting power pulses.
I developed a gauge tester to make diagnosing these issues easy. I think you need one. If the gauges were left pegged very long it is likely that they are not going to be accurate any more. The tester can verify that and also the operation of the IVR. Then Rocketman can recalibrate them for just $15.