I have a 1996 Cadillac Deville. When My tail lights are on my right brake light goes out and my left brake light dims. But both brake lights work fine if I don'thave on my headlights and tail lights. I already replaced the brake light switch and the bulbs. Next I was going to replace the turn signal switch. But I was told it might be a bad ground too. I'm trying not to have to go to a mechanic and fix this myself because I'm short on money at the moment. What else can it be?