Mine was just a bunch of wires with harnesses on each end, and it came with very good instructions. It was from Crutchfield.
Anyway, the HU end is easy enough, just plug it in. Then run the wires behind the dash, under the door sill plate, then behind the cargo area panel to the amp. I have to almost fully remove that panel to be able to get to the amp, and the instructions showed were every screw was. The only hard thing was having to remove the seat belt bolts, I didn't have the T40 and T50 driver bits that they were.
All in all, a simple project. Not hard, but just PITA due to the time involved and dealing with the huge interior panel.