so a couple of things.
first, I thought you said in the original post that one of the VR cause it to peg when you turned the lights on.
IS that not the case?

Second, it could still be the ground, because you are 2 or 3 times removed and each could have paint insulating it.

Circuit board, to cluster, cluster to dash, dash to column or frame.

Put in a new ground directly from the battery to the cluster and see if it still does it.
This eliminates plain ground as the issue and then points towards circuit board or wiring.