Originally Posted by DDMs website
One side doesn’t turn on reliably or at all: This is likely caused by a defective bulb, ballast or an issue with the stock wiring (available power). To identify the responsible component, please swap bulbs or ballasts from one side of the vehicle to the other; if the problem follows one component then that is the part responsible for the failure. If all of the components prove to be functional on one side of the vehicle then you likely have a powering problem on the side that is failing; this will likely be corrected by installing an accessory HID harness.
Intermittent firing for both sides: If it takes multiple on-off cycles to get the HIDs to turn on, you may have a powering issue, which is often resolved by the installation of an accessory HID harness. Also, sometimes increasing the headlight fuse by 5 amps solves the problem.
If you have an HID Harness (whether it's an accessory or H/L harness) installed and are still getting intermittent firing, double check your power and ground cable connections.