[BMFGTO]

My gas gauge on my 69 does not work even when i turn on the key but when i turn on my headlights then it goes past full my dimmer on dash does not work and when i turn the light switch to left to turn on dome light it does not work but when i open door works. I disconnected sending unit at trunk and looking towards gauges i see voltage only when pull lights on. im confused if its a grounding problem or a light switch problem. wondering if anybodys seen this before?

[getmygoat]

definitely one or more grounding issue - get electrical diagrams showing ground points or search electrical forum.

There is a ground bracket behind wiper switch that often gets left off... check that first - but it sounds like there are more issues.

[2002Z4CSS]

Another vote for a bad ground.

[Peter Serio]

All GM fuel gauges have 3 points of electrical contact. One: 12 volts of "+" power from the battery when the key is turned on. Two: ground at the dash cluster and Three: a tan wire that runs from the back of the gauge thru the printed circuit plug-in to the fuel tank sender. From there the sender has a black wire to ground underneath the trunk pan. This completes the circuit so that the gauge reads the resistance at the sender to give you your display.

All GM fuel tank senders in Lemans and GTO cars from 1965-on have a span of from zero to 90 ohms resistance. Zero meaning empty and 88-to 90 ohms gives you Full on your dash gauge. If the ground at the dash is weak or bad that or the printed circuit is starting to go bad and you add 12 volts to ask the dash lights to come on this will tax the cluster and cause the fuel gauge pointer to move. (It will then give you a false display.) Asking your dash lights to come on changes the current flow in whatever ground may be left, or absent. This will cause the gauge to "try" and ground thru another pathway; even if that pathway is thru a lamp filament. Electricity always seeks the path of least resistance.

I would check your printed circuit, ALL your dash ground straps. I would also recommend that you double-check your grounds at both the engine block-to firewall and battery cable just to be on the safe side.

[Txbobcat]

Four in a row say ground

[BMFGTO]

Thanks for all input ill check all grounding points. i was just confused when only reacted when i pulled the light switch.

[Peter Serio]

Check these out, if anyone has even taken out your dash, chances are one or more of these metal straps could be missing.

[BMFGTO]

Thanks, Yea I pulled my dash and had just dashes refinish it came out great, and also put rally gauges. hate to have to pull it again ill see if i can see all grounds from under dash. Thanks for information Steve.