Fuel gauge not working

Rocket Car · 10:29 AM

The fuel gauge is not working on my '74 and has never worked since I purchased the car.

I have fitted a new sender unit and that has not fixed the problem so I guess it's the wiring or the gauge. I have read many of the threads on this but get confused how to test it.

Can anyone share an easy method to check the gauge is working and and how to test the wiring. I cant see any due related to the gauge function.

Thanks in advance!

jbell959 · 01-21-2024, 09:52 AM

I would remove the gauge from the dash but leave it connected.

- If you have a multimeter then turn the key on (car doesn't need to be running) and check that you have 12V between the connector marked '+' and the case of the gauge.

- If you have 12V then remove the sender wire from the connector marked 'G'. With that wire removed, the gauge should read at or below empty. Then take a screwdriver or piece of wire and touch from the 'G' connector to the gauge case and the needle should go all the way to FULL. If it doesn't then the gauge is bad.

- If the gauge is working then remove the connector at the sender and do the same test on the female pins in the connector. I don't recall which pin is the sender and which is ground so you'll need to look that up if you get this far. If the gauge behaves properly when the sender wire is connected to ground then it's your sender. If the needle doesn't move then you have a wiring issue.

Rocket Car · 01-21-2024, 10:57 AM

Quote:

Originally Posted by jbell959

I would remove the gauge from the dash but leave it connected.

- If you have a multimeter then turn the key on (car doesn't need to be running) and check that you have 12V between the connector marked '+' and the case of the gauge.

- If you have 12V then remove the sender wire from the connector marked 'G'. With that wire removed, the gauge should read at or below empty. Then take a screwdriver or piece of wire and touch from the 'G' connector to the gauge case and the needle should go all the way to FULL. If it doesn't then the gauge is bad.

- If the gauge is working then remove the connector at the sender and do the same test on the female pins in the connector. I don't recall which pin is the sender and which is ground so you'll need to look that up if you get this far. If the gauge behaves properly when the sender wire is connected to ground then it's your sender. If the needle doesn't move then you have a wiring issue.

Thanks for this!!!

Will do those tests and report back :-)

Rocket Car · 01-24-2024, 10:02 AM

I did the first test and measured 12v on the plus +!terminal to the case.
The next check from bridging terminal G to the case, did not make the needle move at all.

Is this terminal G?

Rocket Car · 01-24-2024, 10:04 AM

The gauge always reads empty but the empty light does not come on.

Fuel Tank is physically full at the moment.

jbell959 · 01-24-2024, 10:15 AM

Yes, that is the G terminal so it looks like you did the test right. Based on that your gauge is dead. I rarely see these gauges go bad so I'm a little surprised. If you want to venture further you will need to remove the rest of the wires and low fuel bulb then remove the 4 screws and pull that fuel gauge pod out. Only thing you can do it check for a broken wire.

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Rocket Car · 01-24-2024, 12:46 PM

Thanks! My friend had an idea to swap it with his working gauge and see if it works. I'm going to try that next as thats an easy thing to do.

FA-18C · 01-25-2024, 03:10 PM

Rocket - John is the Yoda WRT gauges. You are in really good hands.

Rocket Car · 01-29-2024, 01:37 AM

Quote:

Originally Posted by FA-18C

Rocket - John is the Yoda WRT gauges. You are in really good hands.

Great to hear

Rocket Car · 01-29-2024, 02:02 AM

Well I have no idea what is going here but my fuel gauge has started working.

When I first noticed this issue, the first thing I did was remove and refit all the connectors on the gauge and sender. That did not work. I then posted this thread for help and did the tests, which failed, as the needle did not move when I grounded connector G.
Saturday I got in the car, turned on the ignition and the gauge went full! I switched off the ignition but the gauge stayed reading full. I disconnected + and G and the gauge was still showing full?!

Sunday I get in the car and the fuel gauge needle was now at empty! It moved up and down with ignition on and off and sometimes it would get stuck in the full position.

I decided to remove and refit all the gauge connections and the sender plug numerous times, and now it seems to be working ok.

I have no idea why it's suddenly working, when the early tests I did on gauge Connector G failed?

The next plan is remove and connect the gauge earth to the chassis to make sure that is super clean .

Thanks for your help all and lets hope it keeps working!