Ground wire goes where? Under dash?

So are we thinking this wire is the ground for the cluster? ...

Please read the entire thread again. No, this is not the cluster ground. It grounds the COLUMN to the dash frame which in theory is grounded to the body.

There are two or three "things" in the column (depending on year and options) that need a ground. Certainly the HORN button must have a ground. Automatic column shift has a shift quadrant which is lighted. Some cars have the light in the ignition. I don't remember if that actually needs a ground but it might.

The CLUSTER on most? years is grounded by the mounting screws of the cluster. You should ADD a wire to a cluster ground point, long enough you can "deal with" and bolt it to the column support or dash frame.