Headlight Switch Schematic

Do you have an ohmeter or continuity checker?
That will be easier than wiring in fuse holders.
Remove the connector at the dimmer switch and check for continuity to ground for each of the thee wires.
If the headlight switch connector is easier for you, could start there instead. Doesn't really matter.

With the headlights connected, there will be some continuity to ground.
If its zero there's a short. If its above zero, disconnect the headlights.

That will also be an opportunity to check the wire condition in the buckets.
Light green was often used for the wire from the headlight switch.
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