Gauge wiring gremlin question

[Caldon]

I own factory built ERA #2058, a 289 FIA Street model with the drop down dash & typical SW street gauge layout. I've replaced the SW Amp gauge with a SW one showing Volts. All gauges and lights function as they should (finally), BUT, the last gremlin is when I flip the light toggle switch on to either of the two positions, the gas gauge "pegs" to the full position regardless of how much gas is actually in the tank. When the light toggle switch is moved to "off", the gas gauge returns to showing the current gas level. I suspect some sort of grounding short, but I don't see any connection between these two gauges in the wiring diagram. What am I missing? Any suggestions are appreciated.

[RICK LAKE]

Caldon How did you hook up the volt gauge? The 2 main wires should be contected to each other with a wire tail going to the voltage gauge. Light should snap right in new gauge. Ground wire needs to run directly to a ground on the car. Don't run it into any wiring behind dash. I think you hooked your ground into the sender curcuit to the gauge or have a loose wire on the back of the dash. It's back feeding. Simple to fix. Good luck Rick L.

[strictlypersonl]

The S/W fuel gauge will show full if the sender wire is grounded. It might also show full if the power to it is interrupted, but that's not likely. None of wires from the light switch will be grounded when the switch is on, so the problem doesn't seem to be connected to the headlights themselves. I would look at how the dash light wires are run to the fuel gauge. The Red/White-stripe wire is powered when the lights are on. Other than that direction, it's a very strange problem.

[tboneheller]

Don't drive at night. LOL!!

[Caldon]

O.K. fellas, thanks for the prompt posting of these suggestions and tips. I've got stuff to check for sure. I'll have to go back to notes and also talk to my "wiring" buddy to fully recall. I know "just" taking the dash "down" and looking at the back will reveal the actual situation but it REALLY helps to have these specifics to check for and fix things as needed. Thank you all. Yes even Tbone! When I have driven at night, I make sure I have a full tank! I could report what I found and did...but that may be down the "winter project to do list" road a ways, but we'll see. Take care everyone.

[Tommy]

Caldon,
Maybe this will help: click here.
Good luck.

[Caldon]

Tommy, thank you. A very interesting read. I'll add it to my check list for sure.

[Caldon]

FWIW, just to follow up, in trouble shooting the loss of both brake lights and turn signals, it seems that the original (?) wiring passes very close to the engine/exhaust and had finally "melted". So re-wiring using a "better" routing fixed both the brake/turn signal lighting problem AND the gas gauge "pegging full" problem when the light switch is turned on. Voila, functioning as it should. Thanks again to all helpful comments.