wiring gremlins

Ive been chasing some wiring problems today with my 71 Swinger. I noticed when driving the other night that when I turned the dash lights up, the temp gauge would peg, turn them down the gauge would return to normal. I went out tday to back it out of the garage and the battery is cooked, stone dead. Does not seem to be taking a charge either. any ideas would be appriciated. This is the second battery I have put in this car.