Will the electrical system on a preditor90 and/or sportsman90 (kids got 1 each) support a head light? I'm thinking about getting a set of fog lights and putting 1 each on the atvs, but I dont want too burn out something else on the 4 wheelers.

Are they equipped with electic start? If so, they will work. Just run them right off the battery.

Couldnt you install some resistors so they dont burn out to fast?

I don't think hes worried about the lights burning out, I think he's worried about the 4-wheeler electronics burning up.

i have 2 words to say trial and error, lol j/k , im not sure i think u could do it without harming anything else

The thing is, these things might not have any protection, whereas a snowmobile has the voltage regulator and the inline fuses. If you use a fuse that is slightly above the amperage rating of the lights, you reduce the risk if you do try it. That way you burn up a fuse and not the windings in the stator.

definately use a fuse. I read not to use anything larger than (2) 20 watt lights or else you are taking more than the ATV can charge back to the battery.