One thing you need to do is use a relay and fuse if you upgraded to H4 and higher wattage bulbs , The stock harness in most of our cars runs all the headlight current through that teeny-tiny headlamp switch, which often comes from the factory with 18 gauge leads with the newer lights you'll be getting a lot of voltage drop. Not to mention that the headlamp circuit is typically unfused - a ground fault/short here will cause serious harness damage. (If your switch isn't the weak point, someplace else will be! here
is a nice write up on a upgrade
and i found this relay kit
that would be perfect!