See that little hole in the bottom of the tape? Helped a buddy out today after he had some issues with his HID kit. All it would do is buzz on startup. Of course he's not the best when it comes to wiring stuff, and often uses masking tape and such to insulate his wires.
Anyways, that hole was on the outside of at least 10 layers of tape wrapped around his not so fantastic solder joints...
Do NOT wrap your solder joints with masking tape. That is the easiest way to a fire or blowing up your ballast or bulbs. HID's use at least 25,000 volts to ignite the bulb on startup, and the voltage can easily arch through the tape.
DO insulate your joints with at LEAST 2 layers of heat shrink tubing, one ontop of the other. It's the safest way for the DIY enthusiast that likes to stick HID's into something that didn't come with them (like his cheapo spotlights).