About a week ago I installed a stereo, 2 4ch amps, w/ a total of about 800w RMS. I upgraded the alt about a year ago to a high output Mr. Alternator alt, and did the big 3 with 1/0ga. Now, when I have my lights on and I decelerate to around 30mph, sometimes I get a drastic voltage drop where my lights almost completely go dim and the car nearly dies. I assume it's a voltage drop I don't have a guage. This happens even when I have the radio off.

Could this be the alternator going bad already? I had the battery checked and it's fine.

 

I feel stupid, the battery terminal was connected tight enough.