Instrument panel

You should make a permanent ground jumper in any case Just look at the cluster. Most mounting screws also ground the PC board traces for such things as the ground sides of the lamps. Pick one (or two) and hook a ground pigtail securely. Make it long enough to get the cluster in / out, and BOLT it to something like the column support.

If you want to lay it on the floor, etc for testing, you can always cut it shorter when done