Check the headlight switch and its wiring, I think the headlight switch is a grounding type, with the switch grounding out relay circuits to make the lights work. I only have the '92 to '95 Factory manuals, so I can't be sure about your '97. I can check how the earlier models were wired up for this if you want. Also, when the problem is happening, you might want to pull over and check the available voltage to the headlight with a voltmeter to see if it's close to what you read when touching the battery posts while the Monty is running. Should be close to altn output voltage.