I would like to upgrade to HID lights in my 2008 Jeep Wrangler. The stock lights aren't bright at all. My question is, since this would be an aftermarket upgrade, what am I looking at here? Is it as simple as swapping in new bulbs? Are there other electronic modifications I would need to make?
Xenon headlights require different electronics to drive them, but they also need different reflectors and also a light leveling system to prevent blinding the drivers of other cars, because the HID lights are so much brighter than traditional lights.
If you look closely at a car with HID lights, with the lights shining on something in front of them, you will see that the lights basically cut off at a neat line along the top, where traditional lights illuminate up much higher.
If you know someone with HID lights, ask them to show you when they start up. The ones in my car move up and down as they adjust to the load in the car, so that a load in the trunk won't cause the lights to shine higher than they're allowed to and blind oncoming traffic.
I had done some research for my old '94 300ZX that I wanted to see if I could retrofit. The kit for them was $3,000 a pair, because of the leveling system and the electronics to drive them.
My solution? I replaced it with a new car that had HID lights. They are totally worth it, they are lovely lights and I find when I'm driving my other car without them I keep thinking "are the lights on?"
Another caveat: Some places are selling "cheap" HID light kits from Japanese models. However, they can't be used in the US or other left-hand-drive places because the left hand lights shine up higher than the right lights, and they can't just be swapped around. The lights for LHD cars are the opposite, where the right light shines higher.
Additional details are available in this related question: KIA Soul Aftermarket Headlights
You have received some good answers here, but none appear to be specific to the Wrangler.
The Wrangler uses a standard 7" round headlight housing with H13 bulbs, and there are several HID kits that will work very well in these housings that will plug right into your stock wiring harness. The HID bulbs will fit right into the housing the same way as the standard H13 bulb. Since both sides use the same bulb, there's no problem swapping them left to right, but there's no point, as the bulbs are identical.
Similar to what mike stated above, once you've installed your new HID kit, you can re-aim the headlights, as there are adjustment screws to allow this.
One thing to note, in order to remove and replace the bulbs you have to remove the grille (simple enough, there are six plastic clips on the top to remove, then you can pull the grill right off) and remove the housings. There's no room behind them to access them otherwise.
As was already mentioned, HID bulbs do require a ballast, but a good kit will come with those ballasts pre-wired to plug into the standard H13 wiring and the bulb will be shaped to fit directly into the housing. You will have to firmly attach the ballast to the chassis, usually with a couple of screws. Since you'll have the grille off, You'll probably find a spot without too much trouble.
My H.I.D. plug and play light upgrade cost me $350 (easy install) and is superior in every way compared to usual factory fit.They don't run hot and as every car I have owned has adjusting screws on headlight surround meeting legal requirements should not be a problem. Makers of these kits usually advise starting engine before turning the headlights on.