I like making things, but in this case, pop into a dealer, a parts store, or the wreckers. The clips and relays attached to the harness would make it a hassle to replicate. I picked up mine from the wrecker, and it came with the plug for where it goes through the body. You'll also get to see where it's supposed to run. Spend your time on something more interesting!!
On the other hand, while you're in there, I tapped into the constant 12V line in the harness to put in a 12V power outlet in the cargo area. It runs through a 20A fuse, so it's nice for running an inverter or a cooler or something. Watch out though, as it's always powered, so it will kill the battery if you're running something with the engine off!