1971 Plymouth fuel gauge repair

I kept having erratic operation of the temperature and fuel gauges on my car, but the gauges and Instrument Voltage Regulator were all good.

The Instrument Voltage Regulator is mounted on the rear of the instrument cluster and drops the 12v line voltage down to an average of 6 volts to operate the gauges. It does this by rapidly opening and closing a set of contacts the same as a turn signal relay, but much faster.

After 30+ years they commonly fail open or closed,. If they fail open everything but the ammeter goes dead. if they fail closed they supply 12v and smoke the gauges quickly.

The other side of each of the gauges goes to ground through some kind of variable resistor in order to provide a display.

Both of my issues turned out to be with the sensing devices, not the wiring or instruments.

Category:

Autos & Vehicles

Tags:

• 1971
• Plymouth
• Valiant
• A-body
• gauges
• gauge
• fuel
• gas
• temperature
• hot
• cold
• overheat
• troubleshoot
• diagnose
• mopar
• chrysler
• dodge
• plymouth
• swinger
• scamp
• dart

[JoshHeathMacElvain]

Just replaced mine on my 71 plymouth sport fury. About 80 bucks off ebay. My car jhas a low fuel indicator device that drops the votage down and I cant find that device. Ill have to search the junk yards for that. I would just replace it while you have it out. Good luck!

[WhoSaidTyler]

@JoshHeathMacElvain Yes, some of these parts are beyond scarce. That sounds like a nice car, good luck!

[WhoSaidTyler]

Well it's like this:

 The trans is leaking...it was sitting on the garage floor and I could have fixed it then. The power steering box is leaking...it was on the garage floor as well. The fuel sender was acting up, I could have repaired it while the tank was out....

HAD I KNOWN ALL OF THAT NEEDED ATTENTION BACK THEN!!

lol...

[JoshHeathMacElvain]

Just replaced mine on my 71 plymouth sport fury. About 80 bucks off ebay. My car jhas a low fuel indicator device that drops the votage down and I cant find that device. Ill have to search the junk yards for that. Good luck!

[clubcar98]

Oh such fun, dropping the fuel tank. I "can't" wait to drop the tank on my car. Need to do some cleaning, and hose replacement. My gauge is also broken, so I will have to do that troubleshooting too.

Looks like this entire sending unit could use a good cleaning.

Don't you just love those issues that require you to take it all apart to find nothing wrong, then put it back and everything is good. Its almost as if it just wanted some attention!