I've ordered a tachometer and a phone mount with usb charger...
I didn't want to splice into the factory harness, those squeeze splices may work, but I don't trust them to last.
I didn't wanting to run wires from the tail light all the way up, not too many places to hide it without pulling the harness and using a roll of electric tape/loom to keep it looking clean.
I don't have the know-how/guts to modify the junction box as is shown in the USB charging dock, switch 12V
thread, although that would be ideal because switched accessory circuits make sense. If
anyone has better pictures of where to cut the trace and/or if the en500a1 circuit board is the same, I'd definitely be interested!
Anywho, I found a switched source in the headlight box... the speedometer light! I don't advise pulling many amps from that circuit because I don't know what it's rated for, but it should easily be enough to activate a NO (normally open) relay and allow me to use the existing accessory plugs.
I unpinned the connector on the speedometer side and soldered jumpers onto the flat area and reinstalled them, they were tight but they fit. These are be connected to the energizing circuit of the relay. I connected one side of the contact circuit to the positive accessory port, the other side of the relay is now my switched (+) source that will be used to power the usb charger and what I suppose is the light circuit on the tachometer.
Should I ever need to remove the modification, it's as simple as pulling the pins again and unsoldering the connection.