Those who've purchased the Putco report that the harness uses low quality china-mart relays. If you're interested in building your own but don't want to source the relays, sockets, connectors, etc. Daniel Stern Lighting sells a kit (RIK-2) that comes with Tyco relays, ceramic sockets and connectors. The only thing you need to supply is the wire.
Here's the link to the kit (you email him and he'll arrange the transaction): Products!
Here's is a wiring diagram and some information regarding relays/harnesses: Relays: WHY AND HOW TO UPGRADE YOUR HEADLAMP CIRCUIT