instrument cluster ground

You can ground the instrument cluster with that ternimal added to the headlight switch only if it is a metal housing ( but then the plastci housings have ground wires ). Anyway.. If you were to pull the right kick panel you would find the heater case ground screwed to the inner panel. You can do the same behind the left panel. Route the ground wire from there to the switch should be all you need. I put a male/female spade disconnect In a ground wire that is attached at panel screws. All you should need is a female connector and a ring terminal and a screw.
A lot of people do route the wire ground right to the column support But they'll need to lower the column to service the panel so their ground that could have been used for testing gets removed.
Hope this makes sense.