It's an aux switch that does nothing from the factory. The other end is behind the panel under the seat. I have mine connected to a 12v outlet to charge my cell.
Originally Posted by dibe
There is a 4 pin deutsch connector under the seat that you can connect an accessory to and that switch will turn it on and off.
I just wired up a USB plug to mine yesterday.
Thank you, thank you and thank you!!!! You all just made my life a little easier
Note: This plug is definitely under the seat area. Not to be confused with the same type plug on the left side, which is a diagnostic outlet (on '08 RoadKing). I mistakenly plugged the accessory into the left side, and got "bus Er" message on my dash when the device was plugged in. Once I located the correct outlet under the seat, the connection works fine. Note: The left fork toggle switch controls the power, when the bike is turned on. Ran a usb under the dash, to the front fork area to power a gps.
HD part 91843-97 plugs into that port. About $20 at HD. Supplemental 12v Power Point
Easy to install power point allows an additional 12 volt power source for electrical accessories powered by a cigarette lighter type socket. Features a water-resistant cover with laser-etched Bar & Shield logo. 91843-97