The website with a funny name
www.easternbeaver.com
has a headlight relay kit that should work for most bikes.
Running a higher wattage(brighter) bulb may overheat the plastic headlight shell or overload the hi-lo beam switch with a higher current draw. the website
www.webbikeworld
covers aux. lighting and louder horn installation.
The website
www.rallylights.com
carries brighter bulbs and shows wiring diagrams with relay.
