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Old 01-19-2018, 01:08 AM   #101
67 Burb
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Re: 67-72 Chevy Truck fuel gauge diagnostics 101

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Originally Posted by Lancialonnie View Post
This is a great write up however I am having a slightly different problem. I know my sender works as it is new and tested. My fuel gauge just moves erratically, it goes from being correct to way past full for a few minutes then back to correct and it may stay there or it may go down to empty then back to past full to correct again. There is no rhyme or reason to this, it just moves all over the place. is it a bad ground? Where should I ground the gauge to make sure I have a good ground?
How is the sender grounded? It sounds like it momentarily loses ground and the gauge goes past full, then it finds ground and reads correct. If it is using the tank for ground, that may be the problem. It needs a ground wire from the sender to the truck frame.
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Old 01-19-2018, 01:18 PM   #102
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Re: 67-72 Chevy Truck fuel gauge diagnostics 101

I have a good ground on the sender so I believe the problem is a bad ground on the gauge. I'm just not sure how the gauge should be grounded, from one of gauge terminals?
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Old 01-19-2018, 02:36 PM   #103
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Re: 67-72 Chevy Truck fuel gauge diagnostics 101

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I have a good ground on the sender so I believe the problem is a bad ground on the gauge. I'm just not sure how the gauge should be grounded, from one of gauge terminals?
The gauge is grounded to the cluster with the lower terminal on the gauge. If it was bad the gauge would give a non reading rather than what you are seeing. Concentrate on what Burb is saying and check the tan wire connection on the fuse panel marked FUEL. The other possibility is the no. 4 terminal on the cluster plug connection. It is the return path to ground for the gauge.

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Old 01-20-2018, 12:51 AM   #104
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Re: 67-72 Chevy Truck fuel gauge diagnostics 101

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Originally Posted by Lancialonnie View Post
This is a great write up however I am having a slightly different problem. I know my sender works as it is new and tested. My fuel gauge just moves erratically, it goes from being correct to way past full for a few minutes then back to correct and it may stay there or it may go down to empty then back to past full to correct again. There is no rhyme or reason to this, it just moves all over the place. is it a bad ground? Where should I ground the gauge to make sure I have a good ground?
If you want to add a ground, you can use the center lower terminal on the fuel gauge itself. Do you have any issues with any other gauges/lights? Also check the ground screws on the circuit board, one by the fuel gauge and one by the speedo. The cluster gets its ground through the connector and through the circuit board. very common burn spot on the circuit board is near the connector plug in. Make sure the circuit board does not have any burn spots and the grounds are tight. Also if the cluster tins have been painted, it can cause a ground issue between the fuel gauge tin and the main tin.

Check all the 5/16 nuts on the back and make sure all are tight. It sounds like a loose ground or bad connection to me.

Share what you find here please.

Thank you,
Tom
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Old 02-06-2018, 12:58 PM   #105
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Re: 67-72 Chevy Truck fuel gauge diagnostics 101

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Old 02-07-2018, 11:46 PM   #106
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Originally Posted by TBONE1964 View Post
If you want to add a ground, you can use the center lower terminal on the fuel gauge itself. Do you have any issues with any other gauges/lights? Also check the ground screws on the circuit board, one by the fuel gauge and one by the speedo. The cluster gets its ground through the connector and through the circuit board. very common burn spot on the circuit board is near the connector plug in. Make sure the circuit board does not have any burn spots and the grounds are tight. Also if the cluster tins have been painted, it can cause a ground issue between the fuel gauge tin and the main tin.

Check all the 5/16 nuts on the back and make sure all are tight. It sounds like a loose ground or bad connection to me.

Share what you find here please.

Thank you,
Tom
Curious about the common burn spot near the connector on the printed circuit, What could cause that spot to burn out?
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Edit: reason I ask is that my fuel gauge (71 Blazer) is stuck below empty, I noticed printed Circuit was burned out on ground circuit next to plug in. Replaced circuit and it burnt out again.
Turn signals are also permanently lit..
Grateful for any advice I’m stumped.
Ben

Last edited by CarpBlazer; 02-08-2018 at 12:09 AM. Reason: More info
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Old 02-08-2018, 12:14 AM   #107
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Re: 67-72 Chevy Truck fuel gauge diagnostics 101

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Curious about the common burn spot near the connector on the printed circuit, What could cause that spot to burn out?
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I am also a bit curious but my thought is it is the closest to the connector but weaker than the wiring in the connector. If any circuit gets shorted to ground, that spot seems to be the weak link in the flow.

While doing my testing, I have fried a few by shorts and that is the spot the burn through.

Maybe some of the others have some ideas. I know it is hard to keep good ones around for long
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Old 02-08-2018, 12:35 AM   #108
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Re: 67-72 Chevy Truck fuel gauge diagnostics 101

Thanks Tom, looks like Iím on the hunt for a short to ground somewhere, Iíll report back once I find out where it is..hoping it will fix this fuel gauge stuck on empty situation.
Ben
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Old 02-10-2018, 03:58 PM   #109
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Re: 67-72 Chevy Truck fuel gauge diagnostics 101

Thank you everyone for your input! It turns out I too have a burned out circuit board. When I reached up to feel what looked like a bad spot, I heard an arc so the battery is disconnected until the new circuit board is installed.
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Old 02-14-2018, 08:02 PM   #110
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Re: 67-72 Chevy Truck fuel gauge diagnostics 101

Ok, so I figured out my electrical gremlin causing stuck fuel gauge below empty. I was having issues with all dash lights (turn signals solid, high beam indicator lit, everything that could light up on dash)to go on when ignition on and as I said above, fuel gauge was stuck below zero.
After checking the whole harness, replacing circuit board (only to fry the ground connection again) and hours of scratching my head..I realized the factory tach hot wire was running from fuse box Ďignition unfusedí port to the upper center post on the tach. Problem is, that upper post is the ground post..Face palm...I attached it to ground and boom, everything works.
Fuel gauge is now working perfectly. Iím now on a mission to find correct wiring for factory tach.
This thread really helped me tackle all this and get it solved, Thanks!
Ben
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