Goldoni 
OK.. I just replaced my bulb too. Did not buy the GM one but soldered in my own.
Anyway, can you still see the LCD display when the radio, or car is on?
What I mean is, the bulb is the backlight to the LCD. When mine was burnt out, you could still faintly see the LCD.
You can also take a 9 volt battery to the new bulb to make sure it is indeed good!
Also, make sure the two metal tabs on the new bulb are tight against the solder pads. You could even remove the bulb and bend them down ever so slightly, to make sure they are tight against the solder pads.
Also, check the white ribbon cable of wires going to that board. Make sure either end is not slightly out of the holders. Make sure they did not get cut on the radio metal case too, possibly from moving them outward to do the job.
