Bearing in mind I have never specifically worked on Pantera wiring: Is the dimmer a coil rheostat? These can test OK when you use low power test like from a multimeter but when you put them on load, they can break down. Is it connected the right way around?
I would fix those two extra connections properly to remove them from the equation, and also trace the extra wire coming off the dimmer as I expect that is a bodge. Also, check the resistance in all the grounds.
Chasing wigglies like this is always a headache.