You can buy them at any auto parts store, or I think Home Depot or Lowes and Walmart. Here is an amazon link that shows what they look like:
https://www.amazon.com/WGCD-Power-Automo...184&sr=8-9
If you type SAE connector in the amazon search box a wide variety of them show up, not just the connector with unterminated wires.
Green is ground on our bikes so you will connect green to the black SAE wire and the other wire to the Red wire. Once you have the connector installed you can buy a number of accessories or adapters that will plug into it. Right now I have a voltage monitor plugged into mine. This one:
https://www.amazon.com/Battery-Tender-08...146&sr=8-3
Or here is a USB adapter:
https://www.amazon.com/Battery-Tender-08...32&sr=8-17
Powerlet connectors and accessories are really nice, but cost more and aren’t as available. Easy to get online. Wiring is easy as it’s still only 2 wires. I have it on my ST1300 as the original owner installed Helibar risers with the Powerlet and Ram ball option. So I have various adapters for that. Otherwise I would have installed an SAE connector and called it a day
Disclaimer: Although Green is ground on our bikes, there is always the possibility of a factory wiring error. Some 2014 models are wired wrong in the tail light circuit, for example. ALWAYS check the wiring with a meter to insure proper wiring.