Time to get out a test light or a meter or start doing some more shotgun replacing of things like the dash wiring, underhood wiring, headlight bulbs, and so on. You can be a parts changer person and hopefully correct the issue or become a logical methodical troubleshooter.
I would see if you have main power going into the headlight switch that then the headlight switch then can send power down to the dimmer switch and then out to either the high beam or low beam headlights.
There is no fuse in the fuse block for the headlights but most of the time the headlight wiring PAST the headlight switch is protected by an internal breaker built into the headlight switch.
The headlight switch also just stops power from flowing down to the dimmer switch and then to the headlights or allows it to flow and no grounding of the headlight switch is required for the headlight operation.
Jim