You're confusing the harness and controller and you need both. The harness is just the factory wiring that interfaces with the plug on the third member. You end up cutting off the other plug and soldering or crimping on the wires from the controller to the harness. The $75 controller from inchworm is nothing more than about $10 in parts you can get from radioshack.
Wiring up the controller on carterman's site is cake. If you've ever hooked up off road lights with a relay, you can do it.
