Hi,
I installed a new speedo cable yesterday and when I was done the fuel gauge seems to be reading 1/2 when I know it is full. It is no longer working.
I am sure all wiring stayed intact...
Any suggestions?
Maybe a ground issue?
Thanks!

Did you have the instrument cluster out? Sounds like you didn't get the ground strap properly assembled at the top part of the cluster. That's a very common issue.

Did you have the instrument cluster out? Sounds like you didn't get the ground strap properly assembled at the top part of the cluster. That's a very common issue.

Hi Dave,
I did have the cluster out but I re-checked all the grounds and the strap. It is just as it was before I did the cable.

Here is what I have found though.

When I disconnect the ground wire that controls the cluster, and if I happen to turn on my headlights while that ground is disconnected, then the fuel gauge drops to "E".

When I re-connect the ground wire, the fuel gauge goes to 1/2 and stays there even after I fill up.
Any thoughts on that?

Kinda sounds like a grounding issue, but it's not that difficult to run through the gauge checks.

I went through this a couple years ago and here's how I checked the gauge and sending unit...........

To check gauge, viewed from rear -
* Pink wire on right is 12v from key. Confirm with test light
* Tan wire on left goes to sending unit
* Center lug needs good ground. Be sure it's grounded

To test gauge ---------------------
Disconnect tan wire, turn key on, gauge should read full
Connect jumper wire from sending unit (left) terminal to ground, gauge should read empty (with key ON)


Now, (this is my personal revision) go get 40 ohm resistor from Radio Shack and add that into the jumper wire line, and go from sending unit terminal to ground. With key ON, gauge should read about 3/8 of tank. If you're reading about 3/8 tank with that 40 ohm resistor in there, then your gauge is fine. Of course, you don't absolutely need to do the test with the resistor in the line, but I thought it was a real easy way to quickly confirm gauge accuracy.


Now check sending unit---------------

First, make sure wiring looks good. Check ground connection (black wire) and clean.

You can do this on car but you need ohm meter. Go to inside of trunk at center and disconnect gauge (tan) wire. Use ohm meter and take reading from sending unit wire to a good ground. If tank is full it should be about 90 ohms. If tank is bone dry it would read about zero. If it's reading, say, 125 ohms or more, it's no good.

Confirm bad sending unit by draining (or adding) 5 gallons of gas and taking another ohms reading. If you had initial ohms reading of 80 (close to full tank) and you drain 5 gallons of gas, then your ohms reading would drop considerably, maybe to about 55. If your initial ohms reading is close to zero (empty tank) than ADD 5 gallons and it should be around 40 ohms. If you are adding (or draining) gas and the ohms reading is NOT changing, then your sending unit needs to be replaced, or the sending unit wiring simply may be bad (broken wire or bad ground)..................

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You are the BEST!

I checked the trunk first. The tan wire waas severed. How? I don't know. I replaced it and I now have a fuel gauge!!

Thanks Man!!!

Cool beans man! Glad you got it. I really shoulda mentioned another simple test, to make sure tan wire was OK from gauge all the way back to sending unit, but you figured it out. That's all that matters, lol......

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Hey Dave...what was the test you were going to mention?

Gary, I was just gonna suggest checking the tan (with ohm meter) wire to make sure it was good from gauge to tank. Joe's wire was severed, but he figured it out.

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I believe JimM has posted a fuel gauge troubleshooting procedure in the Electrical Basic sticky for others that may be searching this topic to follow.