I don't know if it is the cause but pull the ground stud out of the inner fender and clean the threads and underside of the nut. I was surprised at how corroded they were.

 

Old news but: 2002 z28 LS1. Lights flicker at night. Changed Alternator - did not fix the problem. Searched for the 7 grounds under the hood. Did not find them where they were supposed to be - looking for 'one under the air box'. Nope. Cleaned a couple that I found - made it worse. Changed alternator to Hi Amp (150). Be VERY careful of connector on alternator for PCM connector to Engine control. PCM tells the alternator when to charge. Did not know it was there and the VERY FRAGILE FRAIL wire broke at the Molex contact. Ordered new Molex on-line. Plenty of service loop on the new connector - not so much in the car. It broke twice trying to strip and twist and solder. Long painful story short - the ALTERNATOR FIXED THE FLICKERING LIGHTS.