in my girlfriends grand prix her rear defog button light dont work does it have a seperate bulb i cheaked the fuses and their fine and ideas?

Yes, there are usually two lights in the defogger switch: one lights up the defogger symbol along with the rest of the nighttime dash lighting; the other lights to actually tell you that the defogger is On. The Defog On indicator is separate from the backlighting bulb (or LED) that lights up the little defog switch indicator (along with the rest of the dash gauges). Which one of yours is out? I'm going to assume here that it'* the Defog On light.

First, is the defogger actually working when you press the button? A defogger sucks serious juice when it'* on, and you should hear a relay click when you press the switch. If not, your problem may be that the timer/relay is not working. (Typically you get something like 10 minutes of power when you first press the button, and 5 minutes for each press after that.)

If you hear a click, and the rear window obviously does defog, and the only problem is that the little light isn't lighting up, then the switch is bad. (I doubt the actual bulb or LED itself inside the button is serviceable.) More likely, though, I think you're not getting any power into the defog circuit in the first place, so look into that. (The fact that the defogger symbol lights up with the other dashboard lights at night does not mean that the defogger itself is working.)

well thanx for the info when i push the defog button on their is no relay switch sound so its probly the relay where would that be under the hood?

Actually in some designs it'* built into the switch itself; others use a remote relay mounted elsewhere.

Sorry, I simply don't know where the GP has its defogger relay. Can you post the year of the car? I'm sure somebody else here can tell you.

99 grand prix se with the 3800 series 2