Dash lights

On the dash circuit board the lamps pick up grounds at three or four different places as I recall. The grounds are made by screws which hold the circuit board to the pot metal dashboard back frame.

Because of this some lamps can have a ground and others may not.

The screws can get loose or the copper paths under them can corrode. I put star washers under all mine so they would bite into the circuit board and make better contact.

To recap, just because you have a good ground to the dash frame does not mean you have a good ground to the bulbs.