Grounding the instrument voltage regulator

And by the way... temp and oil gauges use the same limiter. You haven't said if those work or not.

No, they don't work.

Where is a good spot on the cluster to attach a ground lead? The cluster doesn't appear to have a ground coming off it, I just assumed it was in the harness that plugs into it.

What are the chances the gas gauge was fried? Are they usually last to go?