A Volt / Ohm / Meter is good for finding dead shorts, but can fool you sometimes. If I was there I would certainly love getting into the circuit with you. This internet trouble-shooting electrical circuits is rough at best.
I measured a lot with my little multimeter. My next step is bypassing the stock wiring as I said. I will fidget with it when I have time. My trips are usually short enough that I do not require fans.