Random dim lights

The only thing the ground on the light switch does is associated with twisting the knob to turn on the dome lamp

The poor ground is AT THE CLUSTER. The cluster is poorly grounded by the mounting screws. There are actually several problems with clusters other than failed components

Remove cluster and.......

1...Add wire to a common ground point under a PC board mounting screw, and bolt that to the dash frame or column support

2...Inspect and clean the PC board harness connector pins, and then inspect them for looseness and solder and repair

3...Inspect bulb sockets, clean or replace, and bend contact fingers for more sure contact. Clean board traces where contact fingers rest. Of course inspect and clean bulbs etc

4....Gauges. Seriously consider replacing IVR with a solid state one. Gauge stud nuts get loose and studs/ pc board corrodes. Replace with real nuts, and loosen/ tighten a few times to "scrub" the board clean

5....IVR can lose contact as the contact fingers are not a good connection to board traces. Solder jumpers across.