Mine are in front of the radiator support, its just easier to do this on an A-body for packaging reasons. I took power from the starter relay (I also have the ammmemeter bypass, etc done to my car), have a 20amp fuse (just one, shouldn't need 2), connected to a 12 ga wire that branches off to the two relays. From there I just interrupted the stock wiring harness and connected the original feed to control the relays and the output to the output of the relays. I made a ground strap that goes to the same post as the parking lights are grounded to. The headlights are now over twice as bright.

With relays though, the idea is to keep the relay as close to the headlight as possible as to minimize the voltage drop (especially if using any factory wiring). I would also make it a point to crimp AND solder the connectors that you use as well.

The more load you get off the factory dash harness, the better!