fuel tank sending

67Dart273 said

Actually, "that can't be." The gauge power is NOT fused, it comes directly off the igntion switch to the cluster. This is the same ignition "run" (IGN1) that powers the alternator field, regulator, and ignition. It powers the voltage limiter for the gauges, and the oil warning light, as well as the brake warning light.

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Agreed. A fuse wasn't that actual culprit.
Lets imagine the dark blue with white has a fault/weak connection somewhere like a welded splice. Everywhere the branches go could show low or no voltage.
Owner states he followed that wire to the fusebox so he likely disturbed the weak link and temporarily corrected the problem. My best guess