I searched some of my threads containing posts on the AI but I find that I have not posted any picks of modding my AI. It is very straight forward. Simply buy a 55 Watt, slim ballast on Ebay or from another source. Almost guaranteed it will output about 42-44 Watts to the bulb. Remove the front bezel and set it aside. Un plug the output wires from the ballast to the bulb. Unplug the input wires to the ballast from the battery and the on/off switch. (be sure the switch is not on to avoid a direct short in the event + and - wires are touched together accidentally) Remove the black plastic ballast tray (two screws IIRC). Then remove the ballast from the tray. Mount the 55 Watt ballast in the tray. To do this, I had to make a small notch on the side wall of the ballast tray to accommodate the output cable. To hold the ballast in the tray, I used sticky-back Velcro - two parallel strips, full width. Stick on the ballast and stick on the bottom of the battery tray. Reinstall the tray into the light, make all the electrical connections and re-install the front bezel. Just remembered, be sure the 55 Watt you buy is not the "long" version like the 70 Watt slim ballasts are. It should be the same or very close in physical size to the typical 35 Watt slim ballast. Maybe I'll take a look at mine tomorrow for some measurements and take a pic for you.
If you haven't checked the focus of the bulb, you might want to try it to see if you can achieve a tighter, longer-throwing beam. There are quite a few threads on focusing HID bulbs.
