[Steve Tinker]

Considering that the headlight switch is the main control device, I would try replacing that switch first - plus its a bit easier to change out than the ignition switch. Without having a single line diagram, I don't know if the ignition switch has separate contacts to power up the light switch, so I would go with the suspecting the light switch.
You can try using contact cleaner on the switch internals to see if that makes any difference, but as both switches are prone to failure, you might be wasting your time......