Need help finding new temperature gauge

Harness connector pins all tested fine - they don't budge at all. The gauge nuts were all a little loose, and I alternately loosened and tightened them some. My soldering skills are terrible, so for now I'm going to leave the VR connectors as they are. They seem pretty solid. The only one a tiny bit loose is the center one, and with the condensor and the VR pushed in, I think the contact is good. For kicks, I tested continuity on the 2 gauges and got a pretty good reading of .015 on the lowest setting for resistance. I don't know if that tells me anything other than the gauges aren't completely broken?

How is the cluster "supposed" to ground? I see 3 separate screws that would go to ground, but by what theory are they supposed to contact the chassis? Through the screws that attach the cluster to the dash? If I had bad ground, I think I'd have problems with my other lights, no?

Thanks!