Mark, I've read that the Xterra factory fog lights are a wimpy 15W. Find some fog lights from a mid '90s Sentra,Pathfinder... and use those. They're glass instead of plastic and are 65W. You do have to cut and splice, b/c the connectors are different. I haven't done this yet, still waiting to find a pair in a junkyard.
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00 Xterra SE V6
07 Civic EX
87 Fiero GT...work in progress