I build motorcycle audio systems and as a result have had to learn how to wire motorcycles for auxilary 12 volt power. They now call me Mr. Ground, when I built my 66 gmc I soldered a ground wire to the housing of every light on the truck, wired it in and used a grounding block at the front and rear of the truck. My lights are very bright and I do not have to go looking for lost grounds. One of the reasons for lighting problems being so confusing is that electricity will find a way to ground, be it through the brake light, turn signals, etc. without proper grounds you are shooting at a moving target. Kieth
ps I did wire halogen front headlights in with relays they work great also.