The wiring harness and combination switch is not made for that load. Make sure you have glass lenses and metal reflector, otherwise it may melt.

Insert a 12V relay close to the headlight (one each for low and high beam in each side), and draw a separate 4 square mm from 12V supply to the relay contacts in each side. Use original wiring from combination switch to energize the relays, and connect the lamps to the switched 12V supply.

You can also buy a fully prepared kit at http://www.bergwerks.com/relay_kits.jsp