Ya that looks like a Bushtec plug in I wired up for someone. Most now are round 5 wire. I carry both ends in stock as well as a Y adapter for under your bike seat so you dont have to cut into your bikes wires. Any questions shoot me an email @ brian@asylumcycle.com

by the way, the extra wire is for a dome light in trailer, at lthe bushtec wiring I did was for a dome light

 

Thanks
I put on a 5-round connector on the trailer and bike.
I figured I could wire the dome light to the tail light circuit. I got the isolator / pigtail with Badlands tail/turn/stop adapter all under the seat somehow neatly,, (already had the Badlands installed)
Took a bunch of combinations with the connectorized wiring to make the trailer and bike lights all work together and the bike independently properly. (No quick turn signal flashing)

 

Every day I'm learning new things on this site, thanks'.