if you have the harness you dont even need to hook anything up to get it to work, ones an optional digital speedometer which only reads in KM's no MPH, because i have it hooked up in my car, and the brown is for ebrake like which you dont even need to hook up anyway, it says it wont work with out it but, it indeed does, and the older harness's do have an external ground that you have to ground, because i had to on mine