These harnesses: are designed to allow you to tap into headlight or fog light wiring inside your housing and extend those connections to the outside of the housing passed through the dust cover. Drill a 7/8" hole in the dust cover, press the wiring through, and use the rubber grommet to seal the hole for a waterproof connection. Compatible with 9005, 9006, 9012, H10 and 9145 bulbs. Similar to the wiring that comes in our HID conversion kits, but specifically a different product designed for a different purpose. This harness set: was developed to extend the OEM wiring through the dust cover on some vehicles so the installer can mount a CANBUS module or PWM module on the outside of the headlight instead of trying to stuff it inside the headlight. Using this harness reduces heat of the bulb and the module.