Fuel Gauge Issue

I am getting no movement on my fuel gauge. I have 12 volts at the sender plug but no gauge movement if I ground the Green/white stripe lead. I double checked the gauge posts and both read 50 to 70 ohms. Any other tests I can do to check the gauge?

You shouldn’t have 12 volts at the sender plug for more than a second or so. It should be pulsing. Unless you have an XR7 and you are measuring voltage at the thermistor connection to the sender.

Yup - green/white stripe is 12v to the low fuel thermistor. Grounding it should turn on the low fuel light. Yellow/white stripe should be the pulsed output to the fuel level potentiometer.

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So I checked the green/white stripe bullet behind the gauge cluster. The female and male both have yellow insulated caps but the female is a light green with no apparent stripe. I get a solid 12 volts at the female with the key in run position. Is this the wrong connector for the dark green/ white stripe or is the female wire just faded. Did not check the Yellow/white at the connector in the trunk.

Just checked the yellow/white. It is pulsing.

Grounded the yellow/white and it did not activate the low fuel warning light. The light does flash when starting.

That’s because yellow/white is the gauge. Grounding it should max out the fuel gauge - but its not good for the gauge to do this. Much better to use a gauge tester to verify gauge at empty, half, and full.

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I understand. I am trying to find out if the gauge works at all. It used to work. Is my connection with the yellow plastic bullet correct?

I’ve not had my gauge cluster off yet so can’t answer about wire connectors there. But to be completely sure I had the correct wires, I would test at the fuel sender connector near the fuel tank. A quick test would be to ground the green/white wire just long enough to verify the low fuel light comes on, and ground the yellow/white wire just long enough to see the gas gauge move towards full.

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Thanks for the input. I grounded the yellow/white and the gauge needle moved to full. That confirms the gauge is working. No low fuel light with green/white grounded. I have the sender laying in the trunk making sure it works before installing into the tank. Does the sender need to be grounded to work or is the constant 12V on the green/white keeping the sender from communicating with the gauge. I assumed I could move the float arm up and down and get corresponding movement at the gauge. Not happening. I will get an image of the connection behind the cluster today.

Here is a image with the yellow bullet connector. The male is the dark green/white stripe going to the sender.

Sender must be grounded to work. With sender out of tank, and grounded, the thermistor in the sender should pull the 12V on green/white wire down to just a few volts and light the low fuel light in dash. If it doesn’t, the thermistor is likely bad. Also with sender grounded, you should be able to move the float and see gauge move (it’s real slow to respond). xr7g428 can fix the thermistor and calibrate the float for you for a real good price. He just fixed mine, and your sender will look and work like new.

Not sure what the concern is with the wiring under dash? It sounds like the wires to the sender have the right signals on them. Midlife can probably tell you more about those connectors though.

Okay. I bought the sender from xr7g428. It is out of the box. I will check it again to make sure it is properly grounded. I will also check the short harness for continuity. Seems like I am getting closer to solving my last electrical glitch.

Checked the 3 prong sender harness. It is good. Ground the sender and still no movement at the gauge. The red thermistor lead reads 4.75 volts and the float lead reads .12 to .13 volts and does not really change much as I move the float through its range.

That isn’t too far off for the red thermistor lead - does the low fuel light turn on? It’s pretty hard to interpret the voltage reading at the float potentiometer because it’s pulsed. But if you put the float at 1/2, the gauge should end up somewhere between F and E. It can take 15-30 seconds for the gauge to respond.

Still no red fuel light. I will double check the light - it is an LED and they seem very temperamental. I do get a brief weak flash when I start the engine. No movement at the gauge but I will leave it on for a minute or so.

Low fuel light should stay on the entire time you are cranking the engine. Problem could also be the low fuel relay on a bracket near the radio.

Does the fuel gauge reading have anything to do with the low fuel relay? Do I have two different issues? I checked the relay earlier and it had 12V coming in and a low light on the test light on the resisted circuit. I guess I will have to get back under and check it again.

Fuel gauge and low fuel relay/light are completely different circuits and should not affect each other.

I kept the key on for 30 plus seconds and no movement on fuel gauge.

I get a flash on the low fuel light as I start cranking and as I end. It does not stay on steady. I know the low fuel light is a source of consternation. But i cannot understand why the fuel gauge is not responding to the sending unit signal.