The instrument cluster uses a variation of the wedge bulb. They are mounted in a twist lock base that plugs directly into the printed circuit board on the back of the cluster. When sold with the base, these are called PCxxx bulbs, for example a PC194 is basically a 194 bulb that comes soldered into a PC (Printed Circuit) board twist lock base. Older GM cars (around '90 and earlier) used a standard bulb which would plug into a separately available twist lock base, allowing you to easily change the bulb since you could re-use the base. The newer ones have the bulb permanently soldered into the base, so when one burns out you have to try and find the special PCxxx version rather than just replace the bulb in the existing base.

If you are going to change your instrument cluster bulbs to brighter ones, I suggest you just get the separate PC wedge bulb base, then you can use any one of the non-PC standard T3 1/4 wedge base bulbs by just plugging them in. You can get the correct stand-alone PC wedge bulb base from GM under p/n 25015169. What I did was to use that base and install a conventional 168 wedge bulb which lights up the background numerals and needles much brighter. If you want you can also replace some of the warning indicators with brighter bulbs also, that way when they light up you can't miss them. I always think about the Tim Allen joke about his wife seizing the engine after the oil light came on... "You mean you drove the car after the light came on?", "I thought if it was REALLY important it would have been brighter or something."

BTW you cant not remove the bulb from the plastic housing (dont ask how i know this )

Trade No. Design Volts Watts Amps Avg. CP Life
161 14.0 2.66 0.19 1 4000
158 14.0 3.36 0.24 2 3000
194 14.0 3.78 0.27 2 2500
192 14.0 4.62 0.33 3 2000
168 14.0 4.90 0.35 3 1500