I tried the 194 5-5050 SMD bulb that i already had for replacing the passenger side interior lights, and tested it on the trunk. Seems to work fine if the key was engaged in the ignition, but with no key in at all, there didn't seem to be enough power running to the bulb, so it didn't light up very much. Oh well, guess i'll just keep it incandesent.
Also, didn't fit for the license plate lights, the bulb is too long for the housing.
So from what I can tell:
2004 Grand Prix
Driver/Passenger Front/Back Interior Lights = 194 5-5050 SMD
Driver/Passenger Footwell Lights = 194 5-5050 SMD or the larger 194 9-5050 SMD
Trunk Light = ?
License Plate Lights = ?
Vanity Mirror Lights = the 31mm LED housing, haven't tested that though
Glove Box Light = 194 5-5050 SMD or maybe the larger 194 9-5050 SMD, didn't test yet
I guess the main concern other than size of the bulbs, is how they handle the electricity. Replacing the bulbs isn't much good if they don't work 100% of the time, or the key has to be in the ignition & turned to 1st click. From what I saw, for the trunk, in some situations, it won't light up to 100% of it's potential, heck, not even 50%. And it would really be a pain to have to wire in resistors to make these things work.
