There must be a control unit (Body Control Module) that commands the wipers on and off. Based on the fact you have changed all but that and the wiring harness I suspect that you have a problem somewhere in the wiring. Connectors at the various ends of the wire loom, or someplace in between with a short. I'm pretty sure access to the wiring diagrams will be needed to resolve this. I believe you can get 'one time' access to the diagrams at All Data?