Another issue(s) with all Mopar dash clusters "in general"
1...Grounding. As mentioned, the cluster is "accidently grounded" via the mounting screws. Attach a pigtail ground wire to a common point on the cluster (some of the PC board mounting screws are the ground trace) and ground that wire to the dash frame or better, the column mounting frame
2....IVR socket/ contacts. The IVR finger contacts can lose contact with the pc board traces. Solder jumpers across
3....Gauge terminals---these can corrode, and originally had those stupid "speed nuts." Apply "real" nuts and loosen/ tighten a few times to "scrub" the contact area and stud
4....Harness connector pins. These are rivet/ swedged to the board traces, and can come loose/ corrode. Clean and solder around them
When soldering older wiring/ terminals especially, use extra liquid flux. Be careful NOT to use anything for plumbing, which is acid core. Search "rosin flux" on ebay, there are folks selling small bottles. This is because Kester only has two options that I'm aware of---larger containers like gallons, or the "flux pens" which don't work too bad. But the pens have a felt tip like a marker and can become "frazzled" and contaminated with use on old wire/ terminals.
I like and still use older Kester "radio" designed solder "Kester 44"