Random flashing problem

So, ive had this reoccurring problem for the past few months, and i cant seem to find out what it causing it. While driving down the road or sitting still with the car running, 2 lights on the dash (brake and battery) will randomly flash on, and when it does the headlights get really bright, until the lights flash off a second later. It only lasts about a second when it happens, and i cant find a pattern to make it reoccur. I disconnected the battery and cleaned all the grounds, both wires going to the chassis, and the 2 going to the top of the engine, as well as all the connections to the battery terminals and the connection at the top of the alternator. I also bought 4 gauge wire and ran extra grounds to the chassis, the engine, and from the alternator to the battery. The random flashing still happens.. any ideas on what it could be?

2013 update. alternator was bad, replaced and no further problems.