[1971LT1SWBPOSI373]

you can also clean the printed circuit plug contacts using a pencil eraser while your there.
I'm in the process of rebuilding my dash panel, last night I threw out a bulb holder because for some reason it wouldn't make contact with the printed circuit. I had a good bulb but couldn't get continuity with the meter.
A quick check for a bad ground would be to put a jumper lead with the alligator clips between your dash panel and a good ground. If that doesn't work then you'll have to pull the dash panel and check the wires.
If you don't know which wires the check on the plug don't worry. Just look at the printed circuit, you can see the 4 bulbs that illuminate the guages. Trace the circuit to the connector contacts and you'll have it, the circuit is in parallel through all 4 bulbs.

Hope this helps, TJ