I have a 1992 volvo 940. The headlights won't turn on. I checked the fuses under the ashtray and they are fine. I was trying to install a stereo in the car and it might have caused this problem. I don't know. There are some big fuses in the back of the fuse box, but don't know what they go to. Can anyone tell me what might cause the headlights not to work?