Gauge light bulb spec?

Try This Guide. Click on-- Replacement Guide http://www.sylvania.com/ConsumerProducts/AutomotiveLighting/default.htm

Replacing these miniture bulbs can be a pain , then sometimes it's easy. The bulbs are in plastic holders, and being old the holders can break. The plastic tits break off, so be careful.

A lot easier with the dash out, but that's a job.

If I remember right, You turn them about a qtr turn Counter clockwise and then pull out. Most of the time, hard to get a hold of.

Once you get the holder out, the miniture bulb just pulls out of the holder.

http://www.forabodiesonly.com/mopar/showthread.php?t=124556

If you look about half way down this thread there is a picture of the back of a Dash. It shows two bulb holders, they are black, which is what you are looking for.
Hope this helps !