1990 Chevrolet Suburban 2500 dies when headlights turned on.

I have a 1990 Suburban that is hard to start, and dies when the headlight switch is pulled out to the furthest position. After installing a sub woofer that wasn't grounded to the frame, it became almost impossible to start the truck even with the sub woofer removed. I also replaced the head unit since the factory was bad, and after doing so the head unit was always on, and the headlights seemed to have switched with the interior lights. The horn doesn't work either, when pressed it creates a spark midway down the steering column, which also causes the truck to shut off immediately. The belt makes a squeal, as it normally would when its close to needing replaced. Just replaced the battery and starter, worked fine until one day it wouldn't turn on, replaced the fuel filter, didn't turn on after that until the next day without doing anything to it, it would start right up every time until I installed the sub woofer and now everything seems to be messed up. This is my first project car, and I have no prior experience. So I do not know what I am doing, I am learning as I go. Any advice is appreciated.