Dash Lights - Gas Gauge Change '65 Wildcat

[WinnieWildcat]

Hi All,  I have a question related to previous post regarding dash lights affecting the gas gauge reading (light switch rheostat).  There's a post on this site originally dated 2/28/19 - Gas Gauge Repair.  Replying to this topic (3/3/19) was 63DreamMachine who stated that when his dash lights were on, his gas gauge gave different readings.  He went on to say that he added a new ground and it fixed the problem.  I'm having the exact same problem with our '65 Wildcat.  If I turn the lights on, park or headlights, with any illumination on the dash, my gauge drops about 1/4 tank.  If I turn the dash dimmer full clockwise (no dash lights) the gauge is not affected.

 

Can anyone give me some guidance as to where to terminate the new ground wire on the lighting end?  Do I attach it to the circuit board?

 

I've messaged 63DM but have not gotten a response.

 

Thanks,

 

Scott

[NTX5467]

Before you do any additonal wiring, you might first get a factory wiring schematic and look at the voltage feeds for the fuel gauge circuit.  On my '77 Camaro, it seems that the volt gage and the fuel gauge work off of the same voltage feed.  If the voltage on the volt gage is not correct, the fuel gauge reads lower.  Might be something similar with the instrument cluster lights on the earlier cars?

 

Usually, there's a ground on each side of the front and rear lamp harnesses.  Start with them.  Then look at the bulkhead connector for gunked-up terminals, which you can clean for better connectivity.  Basically to put these things back into "near-new" condition.  THEN, if needed, you might remove the headlight switch and ensure the connectors are clean and tight.  Plus the variable resistor for instrrument panel lamps' brightness.  I'm not sure what could be externally grounded to make things work better, considering that the headlight switch is "voltage in, voltage out" in nature.

 

If you get a reply on that earlier thread, please advise.

 

NTX5467

[WinnieWildcat]

Update on the mysterious gas gauge behavior when the dash lights are on.  March has provided some nice weather to get out to our unheated winter storage garage and finally trouble shoot the problem.  I added an additional ground wire to the ground post on the gas gauge unit and the dash frame.  This has corrected the problem we had where the gauge needle would drop 1/8 to 1/4 tank when the dash lights were on.  The gauge is now stable regardless of the lighting and reading accurately.