My 71 Cuda has decided to not start. It has started and ran fine up until a week ago. When I turn the key, the seat belt buzzer and dome light come on like always, the engine attempts to briefly turn over and then I lose all power to the car (seat belt buzzer doesn't work and dome light isn't on). I checked the battery and it is holding 11 volts. I removed the negative battery cable (it grounds to the body and to the engine), made sure the terminal was tight and re-attached. Power to the car returned but when I tried to start it, it did the same thing and power to the car disappeared. At one time I thought it may have been the starter relay, so I replaced it, with no change. The last time when I tried to start it, I noticed a small puff of smoke appear near the negative battery terminal. I also tried to attach a jumper cable to a ground on the engine and to the negative cable to see if maybe the cable was bad, no change. Any ideas what could be causing this?