The HD Power Relay provides a direct 12v power source to your HID headlights. The HID bulbs are power hungry and rely on a constant and strong 12v source. Do you need this? Not necessarily. Will your headlights work without? Sure. But is this good peace of mind knowing that you have new wiring going to your new headlights? Yes.
The ends of the relay harness are all labeled to make installation as simple as it can get. But if you do not understand how a relay works, please take your time to fully understand what this is. I cannot walk everything through installing a relay harness.
All connectors on the relay harness are the 9005/9006 connectors. These are the same connectors used on the US Ellpsoid equipped cars. Not sure your car has these connectors? Compare the connectors on your car to the infinite images of the 9005/9006 connector on the internet.
*These can only be orderd with a Retrofit Kit - not separately.*
If you know your way around a car, these will likely be very straightforward to install. But please do your due diligence before purchasing. Understand what a sealed beam headlight is, what it takes to swap to a projector assembly, etc. I'm happy to answer questions, but please take a few minutes to browse some forum posts or read through the tutorials.
All HID components and relay harnesses use the 9005/9006 style connectors found on cars equipped with US Ellipsoids. If your car does not have these style connectors on it, you will need to modify your car's connectors or make adapters.