Not used in any modern ap's that i know of, and only used in some models back in the day. Think our hood tachs are one example. Some side markers and instrument clusters on Buicks and Caddys, etc. Parts storse can order thier own brand. Just tell them 168 "clear" bulbs. Also any GM dealer. Part # is 9425542. Come per 10 in box. $1.32 ea, so $13.20 plus tax.
I went ahead and bought some of the bulbs that he experimented with.
The huge one on the left is for me to experiment with as a parking/tail lamp. The next two I'm going to see if they fit into my blinker sockets and under dash courtesy sockets. The two after that I will try to fit in the hood tach. The rest are for the dash.
Update - I bought a variety of LED bulbs. I've been pretty happy. Some were disappointing. (As Dave pointed out, the ones intended for the tail lamp don't output much light)
I'm still experimenting - my printed circuit is crumbling so I can only get a couple of bulbs going on my dash. I'm about to fix that, though.
Bought everything from autolumination, except for a couple of other bulbs that I ordered (and haven't tested yet) from Firebird Central for the dash ( LIG-903 ).
I can put a rundown together shortly.
1968 Firebird 400 Convertible Original: Engine, Intake manifold, Heads, Body, Stereo, 3.08. THM400. Engine rebuilt by Ken Keefer early 2012. New: Holley 4bbl 670 HP, hidden iPod setup, RobbMC mini starter, A/C, front disc brakes
I had the same issue with my Speedo and Fuel gauge, where they were hard to read at night. I tried some cheap led 194's that looked just like a cluster of the radio shack type led's you can buy. Those were no improvement. Then I bought a set of the hi-intensity square looking led cluster types and the gauges look like those pictured now. A big improvement!
