I have a 2002 Olds Intrigue. It has two problems … and neither one is me. (1) When I’m driving down the road, the dashboard lights / headlights will dim & then brighten; dim & then brighten. I feel just a little bit of lag in the gas peddle, but it has never stalled on me. It has had two new alternators installed since I’ve had it, along with the battery replaced a couple of times. Any clue? The other problem is this: (2) In March, I got stuck in a snowbank. The car has a feature called “Traction Control”. Ever since I managed to get myself “unstuck”, my dummy lights on the dashboard go crazy – Trac Off / Anti-Lock Brakes / Service Vehicle lights all come on and stay on. And, the car will make funky noises when I creep to a stop OR try to take off from a stop … feels like the traction control is trying to work because of the noise (usually what it sounds like if I hit a patch of ice in the winter, but there’s no ice this time) … and the brake / gas peddle vibrate … sometimes I have to stomp on the brake in order to make the car stop. My mechanic has tested the car / checked it for error codes / had replaced the brakes prior to the problem … nothing shows signs of wear or fault. Any clue?
Try cleaning the battery connections and make sure the fan belt is tight. As for the brake problem I would suspect a speed sensor ring connection problem on one of the wheels.
A mechanic could put a voltage meter on the battery and determine if the headlight dimming corresponds to a drop in voltage at the battery. If not, the dimming would have to be caused by something other than the battery/alternator. Like a faulty headlight switch, headlight relay (if you car uses one), or electrical connection problem at the headlights or ground.
If the dimming corresponds to fluctuations in the voltage at the battery, then both the battery and alternator would be suspects. Both are easy for a mechanic to test.