Hello, first time poster here. Got my Fist today. Bottom of post for background.
To the topic: having the one hid bulb go out is very common for HID retrofits or modifications. I can't remember off the top of my head but if you search you will find you need to run a relay and get your power directly from the battery for the light, connect the control part of the relay to your headlight switch and ground on the lights to an actual ground point; not a splice or existing connection. It is always a bad idea to piggyback from original head light power and ground. If you have already done this you should search for this problem in general, not particular to the Fist.
Also in agreement with other in this thread: Using HID's in a halogen housing is a very poor choice, for the reasons listed below:
1. Worse for everyone else on the road; due to the poor reflection of the halogen housing. Light scatter is everyone's enemy and it just screams to any car guy that you are ignorant about lights or worse just don't give a shit about anyone else on the road.
2. Although the headlights appear brighter, your distance is lower. This is due to HID's being designed to be projected (hence the name projector) not reflected (halogen, incandescent). So again you perceive that they are better but they are just lighting up everything around you, not directly down the highway.
3. The higher kelvin rating (higher than 3500k) is actually worse for viewing distance. When the light begins to look blue, you are already losing distance. Yellow is the best, and white is a good halfway point between asthetic and function. 4200K is where you should draw the line, its give the nicest a appearance with the least amount of drop-off.
4. The lens in Halogen housing are cheaper and designed for halogen, they will eventually yellow from the HID's. This is also an issue in cheaper cars such as KIA's and not limited to mods.
You can google all the things i've mentioned.
I am new to fist but old hat to the modification community. I had a mildly modded '07 mazdaspeed 3 (400whp DD dyno), '03 stock Focus SVT-used, currently have an '14 Audi SQ5 (stock), '08 Evo GSR 570awhp on 94oct fully built and a Chevy Avalanche with 330,000KM. Got the fiesta to replace the Focus.