When the low beam is on the violet wire will be hot. In high beam the violet goes dark and the red wire should go hot.
I'd run a fused hot to the dimmer input and see if you get any action at the headlights. Will help you figure out where the issue lies, upstream or downstream from the dimmer switch.
The ground get double the load in high beam on 4 headlight cars with stock wiring IIRC.
The headlight wiring circuit on these cars sucks in factory form. Voltage dropping POS
