ok im not sure if dodges have the same thing but my uncles ranch truck did the same thing it is 76 ford. Any ways it was the ignition switch. It had a fusible link in it. and every time it heated up it would split. then it would cool off and go back together it did this until it just stop working completly. All i need to do it replace the ignition switch. It sound like the same problem as yours. Not sure if this help you or not but it can't hurt to check.