[ossiblue]

The implication in your first sentence is that this is a new situation. I will assume that it is happening to only one light circuit, correct? The wiring for the 72 is pretty straight forward for the headlights so I would suspect you are shorting to ground on the main beam circuit.

Check all connections at the headlight to be sure they are insulated. Check also at the fuse block. Check the continuity of the wire for the main beam that is blowing a fuse--wiggle the wire with the continuity tester attached to see if you find a break or ground fault. Also, check the dimmer relay for ground faults.

100w bulbs should not blow the fuse, but they are too much for the stock wiring/switch set up. You should put in a headlight relay system and a heavier gauge wire from the relay to the 100w bulbs to prevent destroying your headlight switch and the switch on the stalk (dimmer.)

Let us know what you find. Help is a web-post away.