To work properly, xenon high intensity discharge headlights require the vehicle's direct current power to be converted to high voltage alternating current. This is accomplished through a ballast, which provides a voltage to the headlamps when they are switched on. A common cause of flickering HID headlights is voltage that is too low being sent to the ballast.
Low voltage in your vehicle's electrical system can be caused by a defective battery, a poorly performing alternator or the use of daytime running lights. In addition, some newer vehicles have sensors that activate by sending a low voltage to the headlights when they are turned off.
A relay harness allows the ballast to draw electricity from the vehicle battery directly, which eliminates low voltage issues. In some cases, a capacitor is needed to work together with the relay harness to ensure proper voltage is applied to the ballast.
High-power capacitors allow increased power to reach the ballast, which will then feed the proper voltage to the headlights. This is the most common fix for flickering HID lights and often solves other problems, such as eliminating the "headlights out" indicator on your dashboard display.
Using a resistor pack will cause the vehicle's electrical system to send the same voltage to the xenon lamps as it would if halogen bulbs were installed.
