This is:
Unfortunately I was unsuccessful with this. The last pic was with two spacers. I ended up having to take one out so that my projector "shrouds" didn't hit the front lens. If I could do it again, I'd find a happy medium and make it work. Now, I'm still trying to find a way to cover the back of the housing and not run out of space. Gotta be able to keep water out of there!
This is a good time to point out that you probably want to get the smallest projectors as you can, space is an issue in almost all phases of this retrofit. I used some Valeo 2.5" xenon projectors. Bi-xenon would be awesome to have, but they are generally larger, and the last thing I wanted was to run out of room. You can find a wealth of info on various projectors, ballasts, bulbs, etc on the message boards of HIDplanet.com BTW- I covered the side gap/holes on the projector with aluminum tape so it wouldn't shed light back into my housing.
Ok, assuming you have one if not two projectors mounted in your housing you'll need to check how level the cut-off is. Hook up the wires from you're ballast to the terminals of your car battery and look at the cutoff line. Originally, I was going to keep the two cutoff lines at the same place like a car's, but decided that I'd make a High and Low beam, so I generally just ride with one headlight on. You won't see much above the cutoff line in complete darkness, so I'd advise on doing this or get bixenons. Here's a pic of my cutoff line, I'd grab a level and hold it to it's cutoff line to make sure it's right, it'll be noticeable if it's not when you have full width of your cut-off. This pic doesn't show the cutoff line color very well, but it looks sweet!
I believe typically your cutoff should drop 4" every 25'. I put mine closer to level. About 1" drop for every 25' of travel. Remember that they will go up when you sit on your bike, but if you use your stock adjustors, you should be able to get them to go up and down some, but try to put your housing close to the correct angle as it will be on the bike so you're at least relatively close. Here's a pic with both on and them set at the same heighth. Like I said, they aren't that way now.
Alright, where are we now, you've probably cussed a lot at this point, so go drink a few beers and start again tomorrow.
If you want it to look real good, you're going to want some sort of shrouds. You can buy the shrouds off ebay, or devise a way to make some of your own. This is what I did. I found some canning funnels and used a 2.5" hole saw to cut a hole in it. I then sprayed it with Krylon satin black finish spray paint. I used the "fusion" kind that is supposed to bond well with plastic. Dunno if it actually does though.
I really like the way it looks and fits. It caused me a MAJOR headache though, because after I had everything back together on my bike, one of the my shrouds brok off. So I had to take EVERYTHING back apart to fix it. Make sure whatever shroud you use won't hit the housing when it's being adjusted. I had to cut a little of the housing away to make this work. I also originally used epoxy to glue the shroud. Epoxy is strong, but doesn't give at all, so that's why it broke. I would advise using 100% silicone caulking. This should hold it plenty well, but have a little "give" so that it won't just break free. It kinda sucks because I had to glue it several times with epoxy before deciding it just wasn't going to work, so it built up a little and from low angles you can see it behind my shroud. It truly isn't very noticeable, but it's about the only thing that looks unprofessional. You can see it here
At this point, if everything went well, you're ready to put your housing back together. You'll need to heat it back up to make it happen. I'd also use a little of that extra silicone caulking to seal it up good.
Here's an original pic of my ballasts and projectors. As you can see, there's not much wire from my ballast to my projectors. I wanted my ballasts in my trunk, and if I was you, I'd do the same. Again, space is an issue, and there's not too many place to mount your ballasts. In order to do this, I had to cut the wires and solder longer wires to it to be able to run it from the front of the bike to the back. I would most definitely solder, just so you don't later get some loose connections and have to look everywhere trying to find out which one is loose. I also used liquid electrical tape on every solder joint to improve waterproofness. I then taped over the liquid electrical tape with regular electrical tape after the liquid dried. All in all you will need to run wires from your regular headlight power to the hot wire on the ballast, a ground wire from the ballast to whatever ground you want to use, and wires from the ballast to your headlights. There are different types of ballasts, and I don't know if they're different, but mine had three wires. So with mine, I ended up having 10 wires ran front to back.