Gas gauge not working

[gnagrant]

I have a ‘74 Duster with a 318. When I bought it, it had a new gas tank sending unit. Before I started messing with it, the gauge would stay showing empty no matter how much fuel I put in the tank. I cleaned and reinstalled the ground strap, and it didn’t make a difference. I ran a hot wire to the tank and it pegged the gauge past full. That might have been a bad idea, as the gauge is showing below empty now.

Do I burn up the gauge by doing this?

 

[67Dart273]

Maybe. Does the temp gauge work? They are both fed off a sort of regulator (limiter) device in the cluster. I assume you do NOT have the ralley cluster. You should GROUND the gauge wire at the tank to see if it moves.

 

[gnagrant]

The temperature gauge was working all along. I haven’t checked it since I started this gauge project. Before when the ignition was on the gauge would move a tiny amount, but never come out past empty. It would go from covering the E to just barely uncovering the E. now the needle is laying on its stop on the left-hand side. I will fire up the car later today and see if the temperature gauge is still working

 

[Dana67Dart]

Do I burn up the gauge by doing this?

Yes.

If you gauge looks like this, it's toast. It might still work to so.evextent but the bimetal has been over heated and permanently bent more than it should be. And the insulation on the wires of the heater are most likely fried as well.


This image is an aftermarket replacement gauge so the needle position for it is normal but it illustrates what a toasted OEM gauge looks like

A good functioning gauge will sit like these two

Here are images of the insides of our gauges.

Note the white, good insulation

Note the burnt black insulation

The gauges are electro mechanical.

There is a heater in the gauge that heats up and causes a bimetal strip to bend causing the needle to move.

Once the needle is pegged to the far left the gauge is toast. (Ask me how I know)

Btw, The gauge gets a ground from the sender NOT power.

Watch and learn.

 

[gnagrant]

Rats. Any place anyone could suggest I find a replacement? Is the gauge removable, or do I have to get a replacement cluster?

 

[67Dart273]

You can replace individual gauges if you can find one. Depending on the cluster design, you may not need that specific gauge, AKA if you find a good temp gauge, you may be able to carefully swap the faces and use the temp ga. "guts" with the face of the fuel gauge, etc

While you are doing this, I would go through the cluster "end to end" and test the gauges with resistors to be sure they are accurate

1...Check the harness connector pins. It is frequent that they get loose/ corroded and lose good contact with the board traces. Clean, use electronic paste or liquid flux and resolder

2.. Replace the IVR (gauge regulator) with a good one such as RTE. Look at the finger contacts where it plugs in. Solder jumpers across from the fingers to the board traces

3...The gauges can lose contact with the board traces. Loosen/ tighten the nuts several times to "scrub" them clean

4...Clean the board traces around the lamp sockets, clean the socket contact fingers and bend them for better contact. Replace bulbs.

5...Find a good common ground point on the cluster and install a pigtail wire say, a foot long. Then ground that to the column support bracket or dash frame.

When you are done, rig the thing to a ground and proper 12V to the proper harness pin, and find/ get/ steal resistors so you can check gauge operation. If you have an old fuel sender, you can manually set it with your ohmeter. Then just apply the resistor from each gauge to ground. They should read the same with the same resistance, AKA the proper resistor for 1/2 scale should read the same on both temp and fuel.

 

[Dana67Dart]

Rats. Any place anyone could suggest I find a replacement? Is the gauge removable, or do I have to get a replacement cluster

Check on eBay, and ad here, I have bought many clusters for the price people ask for a single gauge.

Look at the back for corroded posts and the position of the needle at rest. I'm batting about 95 with those two criteria

I'm not families with the 74 cluster gauges part numbers but there are part numbers on the gauge face that you can search.

Use 2 nuts jammed together to prevent the posts of the individual gages form rotating.

If your cluster is like a rally cluster some of the gauges might rotate opposite of others but what 67dart273 said is generally true about face plate swapping.

Also there might be aftermarket gauges but they might require a particular sender and might look different to other gauges in your cluster

 

[RustyRatRod]

I have a ‘74 Duster with a 318. When I bought it, it had a new gas tank sending unit. Before I started messing with it, the gauge would stay showing empty no matter how much fuel I put in the tank. I cleaned and reinstalled the ground strap, and it didn’t make a difference. I ran a hot wire to the tank and it pegged the gauge past full. That might have been a bad idea, as the gauge is showing below empty now.

Do I burn up the gauge by doing this?

Probably so, yeah. All you had to do was GROUND the wire going TO the sending unit. If the gauge is good, it will go to full. So shootin 12V to it probably did it in.