[RustyPile]

Reversed or "misconnected" wires at the dimmer switch will not cause this problem. The hi beam indicator wire is connected to the hi beam wire at the firewall connector. The dimmer switch does not "care" which terminal is taken for the hi beam or lo beam. As long as the light blue wire from the headlight switch is connected to the dimmer switch common terminal. The tan wire carries the lo beam current and the light green wire carries the hi beam current.. Reversing the wires at the headlight bulbs will not effect the hi beam indicator operation, BUT the wires being reversed will cause the hi beam indicator light to operate in reverse. As I stated, light green wire is for hi beam and tan is low beam.

Bullington, as Pbfut suggested, the problem is probably a poor or missing ground for the instrument cluster, and/or the hi beam indicator bulb socket.