Spent this evening crawling all over this dash. If there is supposed to be a ground at the the mid-structure, I'm not seeing it. At all. The only wiring going through there is either for the column or the brake light switch, and none of it is hard-mounted to the mount in question. Short of pulling the kick panels, I'm out of ideas. I'll do that in a couple of days when I get time to work on the Charger again.

EDIT - You said that cluster grounds at black wire at the 6-pin connector (CI 5, H4 20BK). Tracing that ground from the panel ground, it takes me to the cluster illumination lamps, the ash tray lamp, the heater panel lamp, the clock, the seat belt lamp in the dash, and the map light...all of which function, as do both turn signal bulbs and the hi-beam indicator. Looking at the three inop gauges, I see the shared ground via the voltage limiter...which means that if the rest of the cluster is working and grounded, what's the issue here? This leaves me two more points to look at:

* CI 4, 20DGN - This is the power wire to the radio.
*The output point at the voltage limiter to the three powered gauges.

Since the radio functions just fine, this leaves me no other option than the power point at the voltage limiter on the instrument cluster, right? Could the ...what is that, a condensor?...be the issue, or would I be looking at a break in the panel? I'll plug everything in next time and see what kind of voltage I get across the gauge points, but I think I have my target zone now.