So what is dim? Are the actual signals dim, or the cluster indicators?
I would guess cluster grounding. They are "poorly" grounded through the mounting screws. Does yours have two PC boards in the cluster? I would remove it, go through and loosen/ tighten/ loosen tighten PC board mounting screws to "scrub" them clean, and then add a pigtail from a cluster ground point, and bolt that to the main dash or the column support. Also while you have it out, remove the bulbs/ sockets and clean around the PC board where they contact, and generally check for cleanliness and corrosion, etc