this might sound silly, but when you turn on you lights, you might also be turning the knob to dim the dash lights... I'm not sure of the interior of a 1998 Buick, but on my 1993 Bonneville, I occasionally turned the dash lights off when I pulled the knob to turn on the headlights

just turn the knob to see if the dash lights turn on, or at least flicker... might just be that switch that gives you trouble