wiring problems 1987 MGM

Help...2 months ago my nephew put a new battery in my car. When you turned on the directionals they would blink until you put the brakes on. Then they would no longer blink. I now have no back lights and when you put the headlights on the directionals do not blink at all (including when the brakes are applied). I have a short somewhere. But where? Help!:banghead:

Those are common symptoms of a bad ground in the taillight circuit. My brake lights on my 98 would blow a fuse every time you stepped on the brakes and the A/C quit working because of a loose ground strap somewhere in or around the trunk. (I didn't fix it, it took the dealer two days to find it)