[JLMounce]

When the sender is disconnected, the gauge pegs full. Most of this is factory type wiring, either original or replaced with reproduction.

Only thing different is the tank and floatless sender that needs it's own dedicated ground.

As is typical for a 1969 Firebird, there is a sender connection in the trunk that is part of the rear lamp harness. it shares a double pin with the license plate light harness and the rear lamp harness grounds to the trunk latch support. From the sender I am using that factory pin and using the same common ground as the lamp harness.

The rear lamp harness connects to the intermediate harness near the trunk divider, then the intermediate harness connects to the dash harness near the parking brake cable. It's then connected to the gauge backing plate via the 11 pin gauge connector to the PCB,

The rear lamp harness is easy to get to, but the intermediate harness requires a bunch of interior disassembly, including up into the dome light. I wouldn't even bother trying to test this as the work required to do that would be the same work required to replace it.