Fuel gauge and amp meter intermittent

[Bulletman]

74 rig with 302 and automatic. Occasionally the fuel gauge and amp meter quits functioning. From what I can tell the issue "may" come from the tank selector switch on the dash, but if so I cannot consistently get it to fix or cause the problem. Suggestions as where to look for a cure would be appreciated.

 

[Toddpole]

Sounds like a ground problem. Check all the connections on the back of the instrument cluster especially the grounds.

 

[Viperwolf1]

Strange symptoms. A bad ground at the cluster would cause the ammeter to quit working but the fuel gauge would read high.

No power at the cluster IVR would cause the fuel (plus oil and temp) gauge to stop working but the ammeter would still work.

Fuel tank switch can cause problems but it can be disassembled and cleaned inside.

 

[Steve83]

Occasionally the fuel gauge and amp meter quits functioning.

The ammeter doesn't function much, anyway. How exactly can you tell when yours quits? Does the needle move all the way to one side? It's normal for it to sit in the middle without moving for a long time.

 

[DirtDonk]

Yep, separate issues.
Most likely your dash switch, or a wire, or the in-tank sending unit are causing some sort of intermittent issue with the fuel gauge.
The ammeter is independent of the normal gauge electrical supply, and if it was either ground OR 12v issue with the gauge, then the other two gauges would do the same thing at the same time.
The only other thing that comes to mind is the gauge itself is acting up. That's rare, but certainly not unheard of.

Paul

 

[Broncobowsher]

The dash switch for the fuel gauge is often the issue for fuel gauge. I know many that have been replaced with generic aftermarket switches. Even remember seeing instructions once on how to rebuild the stock ones.

Amp meter is completely unrelated. It is purely a passive gauge. The main battery feed passes through a loop on the back of the gauges. When the battery is charged, it should be reading zero. Minus means you are discharging the battery, positive is recharging the battery. Don't want too much positive for too long, that is overcharging the battery (destroying the battery).

 

[Bulletman]

The two shoupd be separate, but when this happens its both gauges. I can tell if the amp meter works by turning headlights on and fan motor and I can see the needle move slightly when I bring the RPM up a bit. I can get by without the amp meter but I do count on the fuel gauge. And I have no auxillary tank at this time, it was leaking badly so I removed it. It sounds like I need to clean or rebuild the selector switch.

 

[Steve83]

So your only ammeter symptom is that you don't see its needle shift when you turn the lights & fan on & off? That doesn't indicate any problem with that gauge.

The fact that you're still relying on it is the main issue. You'd be MUCH better-off doing the MarsChariot voltmeter conversion described in this & the NEXT several captions:



It's a ~$20/2hr mod, but it's worth double that.

 

[Viperwolf1]

And I have no auxillary tank at this time, it was leaking badly so I removed it. It sounds like I need to clean or rebuild the selector switch.

In that case, just bypass the switch. There are two orange wires going to it. One has a red connector (from main tank sender) at the switch and the other is blue (to fuel gauge). Follow the wire with the red connector a couple inches and you will find it's a short jumper wire with another connector in it. Unplug that connector and you should be able to connect that orange wire directly to the gauge.

 

[Bulletman]

Thanks Viper! Will work on that this weekend