[JLMounce]

Recently I started to get some wonky behavior from the gauge cluster in my 1969 Firebird. Erratic fuel level, or non-erratic, but reading lower than actual fuel level. Additionally the lights were dimmer than typical and exhibited a willingness to get brighter if the car hit a bump or otherwise jerked around.

This seemed obvious as a ground issue back there. I removed the dash bezel and did notice that the screw that attaches the gauge housing to the ground straps on the '69 dash bezel could no longer adequately tighten the ground strap to the gauge housing.

I cleaned up the ground straps, added a new fastener and an auxiliary ground that is now mounted to the dash, as well as the OEM ground straps. Upon reinstallation of the dash bezel, the lights are working great now, but the fuel gauge is still reading between 1/8 to 1/4 low. It's not pegged full or empty and does swing fully, so I know the gauge is working, it's just inaccurate.

I knew that I had around 1/2 a tank, or there about. Testing the sender itself, it's showing 35ohms. Near where I was expecting actual fuel level, so I'm fairly certain I don't have a sender issue (2.5 year old Tanks Inc floatless sender).

I then measured at the dash connector from the intermediate harness and I'm seeing 31ohms at that connector on the intermediate harness. This and the rear lamp harness are the only wiring original to the car. Everything else, including the dash harness is about 7 years old.

Am I wrong in thinking my issue here is likely that the old wiring has simply oxidized and is adding resistance in line between the tank and the gauge?

Visually the printed circuit board is in good condition without any obvious breaks in the circuits, but it is of course 56 years old.

I can't get under the dash in a way to check ohms are the gauge itself to know for sure if the circuit board is bad.

Before I load up some cash in the parts canon for a printed circuit, intermediate and rear lamp harness, is there anything else I should be checking?