Allow me to add a comment of great value. The huge clue that was overlooked is you found 12 volts at a point, until you tried to get current to flow in that circuit by turning on the ignition switch, then it dropped to 0 volts. While this particular problem might not agree here, this type of problem shows up entirely differently when using a test light instead of a digital voltmeter. The cause is undesirable high resistance in the circuit. This is real common in radiator fan motor circuits that are protected by fuse link wires. When those burn open, they leave a carbon track behind, inside the insulation. That carbon will conduct enough current for a voltmeter to "see" 12 volts, ... Until you try to run the fan motor, then, that current causes the 12 volts to be "dropped" across the carbon, and you see the left-over 0 volts at the meter.
A test light works by having current flow through the bulb's filament, and since enough can't get through the carbon, the test light shows 0 volts whether the fan motor is turned on or not. That makes inexpensive test lights much more accurate for diagnosing this type of problem where there is not a definite break in the circuit.
You can equate this to standing on a garden hose and blocking 99 percent of it. A pressure gauge at the nozzle will still show full pressure as long as the nozzle is turned off. Turn that nozzle on and try to get some current to flow, and the little water will dribble on your shoes because the pressure has dropped to nothing. All of the pressure is being dropped across the resistance, or restriction, under your foot.
Had to share that wondrous story. Happy you found it and solved the problem.
Sunday, March 3rd, 2019 AT 5:23 PM
