I've got a 79 bronco with the 400 engine my son and I are restoring. Yesterday it wouldn't crank after he took it to school. The battery was swapped and it started without difficulty and he drove it to work. It was dead again after work. The dome light and dash lights would come on for a few seconds then go out. The battery has 12.5 volts and is new. I have tried to find the problem with a circuit tester without luck. All the wires shows to be good. I'm stumped. Any suggestions?