Does your car have fog lights OEM? if so, use that wiring.

How do your Halo's turn on? Switched separately? Powered on with the side markers? The power draw from them should be negligible.

The OEM halogen bulbs dissipate 55 watts. 55 watt HID's should be the same-no problem with using the main housing connector/wiring. There are a couple of threads (sticky's?) on this install. I wrote one of them.

If you feel that a relay is the way to go, the small, square, flat box in front of the battery opens up to expose a power tap area. I used mine to power my sub amp. Just MAKE SURE to install an appropriate fuse. The power taps there connect directly to the (+) battery terminal.

You could get rid of the mess in your fusebox and power all from there. Cleaner and neater. And it's made for this.