What is included with a HID conversion kit?

A typical HID conversion kit includes:

• two bulbs
• two ballasts (with built-in igniter)
  
• wiring harnesses
• two relays
  

The bulbs don't really need any more explanation.  The ballasts are small boxes (usually one per bulb) that convert the car's 12VDC into high voltage AC required to illuminate the xenon gas. Usually built into the ballast is the igniter initially required to start the bulb.  The wiring harnesses allow you to plug directly into your exiting car wiring with a minimum of splicing wires.  Relays are sometimes included as well, one per ballast.  They use the 12V from the original bulbs to switch in a lower resistance path to 12V to power the ballasts.  They aren't always need.

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