Well fellas, I'm at a complete loss for words. I de-pinned the interior power wire again, soaked it in vinegar+salt solution for 10 minutes to eat away any corrosion, sprayed it with brake cleaner, dried it off, and then scuffed it up with a wire brush and a tiny file.
Barely any improvement. I'm talking hundredths of a volt.
I connected the wire directly to the power connector on the engine-side connector and it
still has a voltage drop directly at the connector. What the heck!?
I tested the resistance of the connector to make sure the outside of the connector wasn't too oxidized. Nope. From inside to outside, zero resistance. I triple confirmed that the engine-side connector had 12.5V. For some reason when you put this female connector on the male connector, I lose about 12 volts (while leaves about 0.35 volts).
Please, if anyone has any ideas as to what I should do (just shy of buying all new connectors) I would really appreciate any solutions to cleaning/repairing these connectors so I can move on from this blasted voltage drop problem. Much appreciated and thanks in advance!
Interior connector. Reading about 0.35 volts when plugged in. Zero resistance through the connector and to the positive wire on the ignition switch.
Engine-side connector. Positive connector on the top-left that's been cleaned and filed. Reading 12.56 volts here.