Sorry, but that's not quite correct. A fuse and its wiring should always be greater than the actual connected load, or you might have nuisance fuse-blowing and/or warm wire and/or over-heated terminations.
A fuse that is to protect wiring should not be larger than the wire's capacity, but both should be greater than the connected load. For a 12.5 amp load, at least 14 gauge and a 15 amp fuse; 12 gauge and 20 amp would be better.
I did not write that he should use a 12.5 amp fuse. I wrote that he should not use a fuse greater than 12.5 amps as anything greater would exceed the current carrying capacity of the MotoLights wiring harness.
He did not provide details regarding whether he is changing to a different size wire than what MotoLights supplies and if so what size. He was looking for what size fuse MotoLights recommends. MotoLights fuse selection can only be based on the wiring harness that they deliver these lights with- not what rewiring a customer might do.
Based on the information that he did provide and the way that he framed his question here is my logic trail.
MotoLights fuse selection is based on the wiring harness that they supply these lights with. They do not provide the wire size but they do state that their wiring harness has a maximum current carrying capacity of 75 watts per light. Based on a two light installation that is using this wiring harness I wrote that the
maximum size fuse that should be used is 12.5 amps as to exceed this is unsafe to the wiring harness. If he rewires these lights with heavier guage wire than what MotoLights has supplied than that is a different ball game.
Based on the maximum current carrying capacity of the MotoLights wiring harness and the maximum wattage light bulbs that MotoLights delivers these lights with I suggested a 10 amp fuse. This still leaves 1.7 amps of unused capacity which should be plenty to prevent any nuisance fuse failures. It also is well below the current carrying capacity of the MotoLights wiring harnesses by 2.5 amps so there would not be any warm wires or terminals either. If he were to use higher wattage bulbs than what MotoLights supplies then again, a different ball game.
Assuming a set up as delivered by MotoLights, as he offered no information to the contrary, is this logic flawed?