92 SL2 ABS light

Girlfriend has a 92 SL2 that gets an ABS lamp come on when she stops. Her headlights also get a bit brighter when this happens. Her cruise control works good. I'm not Saturn expert (thus the questions), but not sure where else to look. I noticed this past weekend that the ABS light stayed on after starting for a spell, then goes away after driving, but not all the time. Generally, I thought maybe a vacuum problem, maybe a low level switch for the brake reservoir (if one exists), or maybe a speed sensor.

Any suggestions would be appreciated.