The easiest and least destructive way is to wire them direct from the battery, via a fuse and relay or fused relay, which I prefer. All you will need to do is take one wire to the main beam of your headlamps and connect with a scotchlock (a tool of satan) or other more reliable method. The other wires to the relay are a ground, the battery feed and power to the lamps, which are then grounded also.
Sorry if this is a bit Janet and Jane but electrics are not everyone's thing, if so you can buy a ready made wiring kit from places like Halfords.
