Gauge Gremlins, need help.

[Fuelman]

Hi All,

First post, great site!  I need some help.  Getting my 71 429 SCJ Drag Pack up and running again.  Fresh motor and car is in great condition always garaged.

Sent the factory gauges in had them checked and redone with white faces.  Added an MSD ignition and blaster coil, had the tach set up to run with the MSD.

Tach and speedo work fine.  Gas and oil pressure work sometimes then stop.  Temp and Alt don't work at all.  Have tested the temp and oil gauge with 3 D batteries (4.5 volts) and they work.  Realized when they put the center gauges back in the housing they switch oil and temp position, so wires were crossed.  thought for sure that was my problem, changed them back today and nothing worked, checked fuses and they were fine.  Man handled the center console gauge harness a bit and then the fuel and oil gauge worked for awhile and then stopped.

I have a nostalgic AC system and electric fans, electric fan control box and sending unit are hooked up where the temp light was hooked up before, I think.

Bit stumped here, any advice / help greatly appreciated.

 

[midlife]

Probably a bad constant voltage regulator or busted circuit board traces for the CVR. Another possibility is that the resistor wire going into the dash cluster connector needs to be re-crimped or may be broken. Gauges are not related to fuses, despite what Mustang Monthly and the Internet says.

 

[Fuelman]

Probably a bad constant voltage regulator or busted circuit board traces for the CVR.  Another possibility is that the resistor wire going into the dash cluster connector needs to be re-crimped or may be broken.  Gauges are not related to fuses, despite what Mustang Monthly and the Internet says.

Thanks Midlife, I did change both the circuit board and the IVR.  Unless one of the is bad, I have heard the IVRs can be an issue.

Any idea what color the resistor wire is and where does it originate from?

 

[midlife]

It is black/green. It originates at the wiper switch and ends at the dash cluster (pin 7 for tach, pin 5 for non-tach) and uses a black wire to help it being crimped at the pin.

IVR's can be bad, and they do need to be properly grounded to work. You can test the gauges by very briefly grounding the sending unit line; don't do this for very long as they can burn up if left grounded.