What would cause my head lights to flicker and also the interior dash lights to? on 1999 Chevrolet Monte Carlo

Doesn't flicker all the time only sometimes

POSS BAD GRD CONNECTION OR PWR LOSS AT TIMES
1 more answer
Does this happen when you push on the brakes? I had a similar problem when i pushed on my brakes and I just unplugged the ABS and it stopped.