Why do I need a relay harness?

Some vehicles might be able to power up and switch HID systems normally without problems for quite some time. 

The main problem occurs over time especially with the dual circuit bulbs systems (ie: H4, H13, 9004, 9007)   Here is why:

The inrush load can be up to max 13 amps per ballast, compared to 7amps inrush when using halogen. The factory design parameters for headlight circuits are 7 amps inrush and 4.5 amps continuous load. Over time, factory connectors, multifunction switches, headlight switches, wiring and fuse holders can slowly degrade, because of heat buildup that occurs during switching on and off the HID systems and switching back and forth  between high and low beam .    

With the dual systems, you will be switching the HID system on and off, plus switching between high and low beams.  All of this switching at the higher amperage takes a toll on the factory switched and gear that is not sized for the added in-rush current of the HID system.

These components are very time consuming to troubleshoot and replace because they are usually well hidden behind dashboards and other wiring and often are very tricky to remove and replace. Parts can cost several hundred dollars.  Add 8 hours labor to that and it becomes obvious that a $25 wiring harness + relay is a good value.  

For this reason, all of our dual circuit HID systems (ie: H4, H13, 9004, 9007) come standard with a heavy duty relay harness that handles all of the high energy switching.  This eliminates any extra electrical load being placed onto your standard factory connectors, multifunction switches, headlight switches, wiring and fuse holders.