Sorry about the lateness of this post everyone. We just had a family member diagnosed with inoperable cancer, and only a few months left. Things have been hectic to say the least. This post had been started about that time, so pictures are from post-install and directions are from memory. YMMV.
I ordered an HID kit from DDMTuning.com. Specifically, I ordered the 35W 9004 (Hi/Lo) 5000k (White) Apexcone kit found here: HID Kits, BMW Aftermarket Bumpers & Lighting, DEPO - DDM Tuning
. I had grown sick and tired of having shoddy lighting, and wanted to dress up the Caprice a bit for not too much money.
I received the package about three days after my order, and the wiring seemed fairly self-explanatory. There's a main harness with three wires(or I assume however many wires your headlight requires) that fit into an adapter to plug into one of your headlight plugs on your car harness. In addition to those wires, there is a 12v+ direct wire and two lines for ballasts and constant supply lines for the HIDs(after initial fireup from the ballasts I assume).
You'll need to find a good mount point for your main harness. Measure out how much length you've got for each lamp connection, and pick a point somewhere between the two lights for easiest installation. A single sheet metal screw should hold it just fine.
Next, run your lamp connections to their respective locations (the longer cord going to the lamp assembly furthest from your battery). Mount your ballasts nearby in any handy area you have that's unoccupied. I mounted the passenger side ballast in front of my battery, behind the lamp assembly itself.
At this point, check your ballast plugs against the ballast themselves. There should be an indicator marking to show your positive line. If your plug is wired backwards (One of mine was... >.<), you'll have to pull apart the connector and flip the pins around. It's fairly straightforward, just don't snap a pin if it feels like they aren't pulling out. Plug in the harness wires to your ballasts, and from your lamps to the harness as well. Mount the black wires with a round terminal connection to your frame for your ground.
From here, connect your positive terminal wire from the main wire harness to your power supply (battery, alternator, pick something).
Now that the rest of that is taken care of, match your three adapter wires coming from the main harness to your old lamp assembly connectors. Plug these wires into the blue adapter in that order, and plug that unit into the old lamp assembly plug.
Start up the car and make sure everything works. If the lights seem bright on low-beams, and dim on hi-beams, flip the two outside wires in that blue adapter connected to the old lamp plug. If you have an old cop car from Flint and the bacon didn't rewire everything after gutting police equipment, you'll have to do this step anyways to make sure your lo-beams are actually low. Those jerks.
Replaced the ridiculously large-grainy photos with smaller ones that look a little better. Call me a stickler for layouts, but I hate it when the forum gets screwed up when images don't scale down.