Originally Posted by GregCifu
Ya' know, you might consider wiring a direct fused line from the battery up to the headlights and using two Bosch relays to turn each (or both) lights on. The factory wiring in my 620 Adventure (and Duke for that matter) is sorely undersized. If you actually put a voltmeter on the bulbs, you'll see that they're only getting around 9-10V. With a full 13-14V the stockers will really surpise you.
I haven't wired mine yet but I did try it with jumper wires straight from the battery and the difference was amazing. Quartz halogen lights are amazingly bright and white when supplied enough voltage. Aftermarket lights aren't going to perform any better without sufficient current to run them. Running both filaments together through the stock harness may overload the wire or the fuse.
Also remember that with both 55W bulbs running, you're sucking 110W. Add 5W for the tail light, another 10-15W for the instruments and there's not much left to run the ignition, charge the battery and run the fan if it kicks in.
I don't know if it's "sorely undersized", but I agree with your concept. My LS fan doesn't run nearly as well as my RS fan which is wired directly off the battery. Hadn't considered wiring the lights direct. Good idea. I'm asking Santa for a pair of the small TT HIDs. If I'm a bad boy and all I get is coal, direct wiring may be a good alternative.