I can't find the fuse box on my Polaris 500--does anyone know where it is??  

sorry it took so long to answer this one i had to hunt my service manual for it.

the sportsman 500 1999  does not have fuses.
it has resettable relays.

looking down at the battery go toward the front about 5 inches and there should be a black pouch.
what happens is this pouch normally gets full of mud and falls apart.
but you should find the relays there and be able to reset them. (just make sure you dry it out good first.  you can also try to water proof it a little with some aquarium silicon