Need ideas with fuel guage not working when cluster installed

sprice

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Have two clusters form 68' 300. Fuel guage not working. Sender tested defective by testing for ohms. Grounded fuel guage to confirm guage is working. Putting all together through test leads fuel guage will work on the floor of the car. Once the cluster installed, needle looks like it nudges, but nothing. Have tested the voltage limiter. Blinks with a test light (I read this means its good, however same setup worked on the car floor. Added grounds to the sender unit in case a ground was an issue. All guages working in the both clusters on the floor with test leads. Installed in the dash, fuel guage quits. Almost like the grounding of the cluster is causing the fuel guage to not register.

Feel like I am missing something obvious. Any thoughts out there?
 

sprice

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Ground, ground the world around...
Will be placing ground wire from battery along body connecting at various spots to ensure good ground throughout. The painter painted everything so I am thinking you are correct. Will post what happens. Thanks.
 

sprice

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Have put a new 4GA cable from negative cable to block and to frame. Ran 8GA cable from negative cable to firewall, cluster mount and to trunk. Cleaned mounting points down to metal. Still no fuel guage working when cluster assembly installed into dash. At a loss.
 

HWYCRZR

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My first check would be the wiring plug going into your gauge cluster. By putting it back in the dash is it pulling or twisting the harness. If you have a cracked circuit board, it could be twisting a little at install opening the circuit. My experience is with a ‘68 Polara, which may be a little different than the Chrysler.
I also made a resistance tool to test my gauges. The beauty of this tool is you can start by isolating the body harness. I unplug the rear body harness located behind the left side vent panel and insert the resistance module going to the gas gauge. One wire to ground the other to your fuel gauge and turn the dial. Power on to your cluster. If it changes the gauge you know that your issue is between the connector and sending unit. If it doesn’t work, you will have to follow the wires up to the panel and check for loose wires or pins or a cracked circuit board.
You can use inline resistor to check gauge as well. 10 ohms is full tank 74 ohms is empty.
Circuit board from ‘68 Polara.
If you can break across the boarder and come to Fargo you can have my spare resistor.
Postage to Canada is probably more than what you can buy it for on Amazon.

‘68 Polara board- fragile and maybe affected by twisting. Pins can also break free.
FC12C80A-D645-439F-B2AA-1723270768CD.jpeg


pot resistor
4405CBE6-3002-495B-BA94-D1C30056DB13.jpeg


high low medium settings for mopar gauges. ( source somewhere on the internet, but seems to work with my gauges)

Front side of my tester. Made from an old Bakelite electrical box.
279B6067-DBFE-4954-BAED-D502E219881E.jpeg
DF6150B0-70C6-4B33-8161-743F14572839.jpeg
27C2A8B6-5CE8-497B-87DF-7D65E3ADF6A0.jpeg
 

sprice

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My first check would be the wiring plug going into your gauge cluster. By putting it back in the dash is it pulling or twisting the harness. If you have a cracked circuit board, it could be twisting a little at install opening the circuit. My experience is with a ‘68 Polara, which may be a little different than the Chrysler.
I also made a resistance tool to test my gauges. The beauty of this tool is you can start by isolating the body harness. I unplug the rear body harness located behind the left side vent panel and insert the resistance module going to the gas gauge. One wire to ground the other to your fuel gauge and turn the dial. Power on to your cluster. If it changes the gauge you know that your issue is between the connector and sending unit. If it doesn’t work, you will have to follow the wires up to the panel and check for loose wires or pins or a cracked circuit board.
You can use inline resistor to check gauge as well. 10 ohms is full tank 74 ohms is empty.
Circuit board from ‘68 Polara.
If you can break across the boarder and come to Fargo you can have my spare resistor.
Postage to Canada is probably more than what you can buy it for on Amazon.

‘68 Polara board- fragile and maybe affected by twisting. Pins can also break free.
View attachment 443970

pot resistor
View attachment 443971

high low medium settings for mopar gauges. ( source somewhere on the internet, but seems to work with my gauges)

Front side of my tester. Made from an old Bakelite electrical box.
View attachment 443972 View attachment 443973 View attachment 443974

Mine is a bit different. No circuit board. What I have done tonight is separately ran a wire from the sender to the guage to make sure no shorts. Both wires: factory and new responded same on the guage. Again guage tested as manual states by grounding sender wire. Sender is 12 and 75 ohms. Dash lights are working in cluster so grounds are good. Only way to get the needle to move is by isolating the voltage limiter from ground. If I place power to the “in” side of the limiter and attach a test light to the VL body, it has a low light flash. I’m thinking the VL is sending a signal through its body rather than 5v post. I’m going to see if I can find a new or used VL to test.

A778196E-8D4C-42F1-9094-1C2A62D8DB2E.jpeg


12C5A2FE-2F34-4BA8-BA3F-684273214C56.jpeg
 

cbarge

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On my 68,I ran an extra ground wire at the sending unit grounded to the frame.
Easy install as a process of elimination. the ground strap reliability from the factory is questionable at best.
So in theory you have power to the gauge.
Check for power at the wire at sending unit.
Hope this helps
 

sprice

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On my 68,I ran an extra ground wire at the sending unit grounded to the frame.
Easy install as a process of elimination. the ground strap reliability from the factory is questionable at best.
So in theory you have power to the gauge.
Check for power at the wire at sending unit.
Hope this helps

I'll try another place for ground source. You start to forget your own testing. Thanks.
 
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