[patrickt]

Perfect. The gauge is showing that current is running through those wires and, somewhere down the line somewhere, that current is shorting out to ground. Once you go past that shorting out point, there's no more current in the wire (usually). Note that the needle swings in the direction of the current's travel, which kind of "points" to the short. If you flip the gauge around 180 degrees the needle will still swing in the correct direction, but it will now be opposite. March down the circuit's wires, watching the gauge's needle, and see where the behavior changes (like no needle movement at all). If the behavior clearly changes after, say, the connection to the tachometer, then remove that connection. If it clearly changes after a multi-wire connector, then wiggle the connector first to see if you can make the circuit breaker stop breaking, then disconnect it completely if you can't. Don't just wiggle wires willy-nilly though, you might temporarily fix the problem and not be able to figure out exactly what you fixed until it breaks again (which will be the next really inconvenient time and place). The hardest shorts to find are frays/breaks that are inside a taped off bundle of wires, or a goofy behaving multi-connector. That tool will point to the offender though. Now that we have disconnected the pink wire at the fuel sender, and the wires and shunt that lead to the charging light and voltage regulator, here is a list of what I think could be causing the fault (other than a broken/frayed wire or misbehaving multi-connector:

Heater Switch shorting out
Wiper Switch shorting out
Wiper Motor shorting out
The "circuit board" that ERA uses to control the wiper parking
Fuel Gauge shorting out
Tachometer shorting out
The Smiths voltage regulator for gauges shorting out (which I did not originally have, but that I then wired in myself solely to power the fuel gauge). Yes, it does make it more accurate.