The best way to run high wattage bulbs is to use a relay that is connected straight to the battery that way you will only be drawing very little current from your stock wires.
Using say a bosch spdt you would put the positive terminal of your stock low beam lights to pin 85. 86 would go to chassis ground pin 30 you would fuse for say 20amps direct to the battery and pin 87 would go to the positive end of you new 100w bulbs.
Basically what is happening is instead of drawing all the power to fule your 100W bulbs from the stock wires... which would eventually melt etc... you are only using the stock wire to "trigger" on the relay which will then draw current direct to the battery for you lights.
Make sure you use proper gauge wires for this as you dont want to cause and electrical fire. Hooking up a light relay like this is basically the same way you would wire up some foglights... same concept They best overkill way to do this is to have a relay for each higher wattage bulb you are gonna run so you need a total of 4 relays. :bunny: