OK, well look
The dimmer switch is a simple, one pole, double throw switch
Headlight power comes INTO one terminal
Power goes OUT one or the other terminal, and when you mash the switch, these two terminals reverse, IE the terminal which had power goes dead, the other terminal becomes powered
High and low beam power go from the switch, THROUGH the bulkhead connector
Power branches off from the HIGH beam wire before it goes through the bulkhead and goes up to the cluster "hi beam" indicator.
So if you have low beams, the light switch is OK, and at least 1/2 the dimmer is OK
If you have a hi beam indicator light in "high" beams, then the OTHER half of the dimmer is OK
If you have power on both high and low beam wires on the engine side of the firewall, then the problem HAS to be in the engine bay harness, grounding, sockets, or "it's possible" that the high beam filaments in both lamps are burned out.