ThePsuedoMonkey
XS400 Addict
The conversion to HID is very simple. You have a few options, but at its core it boils down to two things: the new bulb and the ballast/controller. The most common bulbs are 35W singles, but these are designed for older cage vehicles. You want to make sure the one you get has a low and high setting, so either a bi-lev HID (usually 35/55W) or a HID/halogen composite. If you buy the ballast separate from the bulb, be warned that most are 35W unless specified otherwise. The ballast is wired for the standard auto bulb sockets (double probe), but the bulbs usually have the adapter for our triple blade connector. If you already upgraded to a halogen, then you just need to grab a bulb that fits the socket to your headlight. If you still have a sealed beam then you need to decide if you want to rig up that to hold the new bulb or if you want to do it the right way and get an enclosure/reflector. I rigged up a 5" off-road enclosure to fit mine a while back. Now the only option left is what color the bulb should be. The rating system for the bulb color is black-body radiation, essentially the color of light emitted by something is determined by its temperature. Since the temperature of the sun's surface is ~5775K, a 5000K or 6000K bulb will get you closest to natural sunlight. If you want something more blue/violet you can pick up to 15000K, or if you want more yellowish you can go down to 3000K.
I moseyed over to ebay and grabbed a 35W ballast
and a composite HID/halogen bulb 
this way I still have a headlight if the ballast fails while riding (I'm a cheapskate). Between them, I only spent ~20 bucks. I removed the rubber sheath on the wires, since it was unnecessary and that gives a little more leeway in where you can mount the ballast. There isn't anything tricky about fitting the bulb itself, even with both bulb types my H4 fit easily into the socket. The wires are routed like everything else, down to where I've chosen to mount the ballast. I found an unused mounting hole in the frame near the tank; pretty much the perfect location.
I'm not sure how the dual HID bulbs work out, but I think you might end up running a ballast for each setting. The ballast itself has a little bit of girth to it, maybe about half a kilo, so that's the trade off for better light and reduced power consumption.
I moseyed over to ebay and grabbed a 35W ballast
and a composite HID/halogen bulb this way I still have a headlight if the ballast fails while riding (I'm a cheapskate). Between them, I only spent ~20 bucks. I removed the rubber sheath on the wires, since it was unnecessary and that gives a little more leeway in where you can mount the ballast. There isn't anything tricky about fitting the bulb itself, even with both bulb types my H4 fit easily into the socket. The wires are routed like everything else, down to where I've chosen to mount the ballast. I found an unused mounting hole in the frame near the tank; pretty much the perfect location.
I'm not sure how the dual HID bulbs work out, but I think you might end up running a ballast for each setting. The ballast itself has a little bit of girth to it, maybe about half a kilo, so that's the trade off for better light and reduced power consumption.
This should be interesting...
