HELP HELP Electrical Problems Im 100 percent LOST With my blazer

Im 100% lost in the electrical problems in my 1985 S 10 Blazer. I had a CD player in a few years ago that would cut out at high volume, and shut off for a few seconds every few minutes for no reason. I thought it was a faulty CD player till I got a new one and the same thing happend. So I re grounded the new cd player, and now it still does it, but now when I turn on my head lights, my interior lights come on, but my taillights do not, they only turn on when I hit the brakes. I dont know if this was because of the cd player or not, but Im sooo lost and broke, cant take it anywhere.. please help!!!

If it all started acting up when you installed the CD player disconect it and see if your problem goes away.

Your cd player problem is probably a safety feature built in designed to stop it from overworking or overpoering the speakers.
You would have been better off installing an amp and better speakers than replacing the deck

Check all your grounding wires, grounding points and bulbs on the whole truck. These trucks are notorious for having bad grounding points and broken bulbs that affect everything else.