Can anyone tell me what the mysterious 4th wire going into the ignition switch is and which terminal it should be hooked to . ? I am trying to bypass the stock ignition and transplant an aftermarket, generic keyed ignition switch,One fat wire goes to theBattery , one goes fat wire to the starter , one skinny wire powers to the tail light, but the other,skinny wire seemingly hot all the the time is a mystery and I am afraid to hook it up to the accessory terminal without knowing for certain what it leads to and where i should connect it on the three position ,NAPA, donor? switch. I can't find a wiring diagram for the ignition of my bmw f650gs and would appreciate any help . Thanks very much. STEVE