Our Road Zeppelin seat's air compressor is plugged into ours. Their was no slack in the wiring harness around the plug, making it almost impossible to use. I cut off the wiring zip ties front and back of the plug, and there was all kinds of slack in the harness. Then retied the harness.

 

On my 2013 Road King Classic the accessory plug is under the seat by the battery. I purchased kit 70264-94A which is a "Y" adaptor that plugs into the accessory plug. I then was able to disassemble one of the "Y" ends of the adapter and tap into the leads to power a USB adaptor I got on Amazon.


For reference on my bike, there are 4 leads in the plug numbered 1-4. Here is what I found with the voltmeter:

1-12v on when ignition is on
2-neutral/ground
3-12v on when ignition is on and aux switch is on
4-neutral/ground

Got everything hooked up and now I can power the USB ports on and off from the AUX switch -- the whole point being to run a lightning cable up to the handlebars where I mount my iPhone with a Ram mount.

Just documenting for everyone's reference as it seems there may be a lot of differences between bikes or just general confusion. BTW, my bike does have two similar plugs under the left cover, but these are NOT connected to the accessory switch as far as I was able to tell.

 

My Love Jugs engine cooling fans.

 

Get out the volt meter again. One of the ones you have listed as neutral/ground is probably another brake light feed. The plugs are usually: on with acc switch, on with ignition, on with brake lights and ground. I don't remember pin numbers offhand.

FWIW there's probably a second single wire plug nearby the 4 pin one that is B+, meaning 12V unfused straight from the battery (or possibly from the main bike fuse) again, memory fails...

 

When you add any additional electrical accessories, you can use this switch to switch them on/off. The 4 pins Deutsch type connection is located under the seat in front of the battery.