Is that the HD aux. line (switched), or a line someone added for a battery tender? Either way, check to see if you have 12Vdc there at the plug. If so, should be fine.
Thanx for the info however I have used the aux (switched) plug under the seat, I'm talking about the plug visable below the seat resting on or near the dipstick. It is two pronged (one visable (male) one covered (female). There is a tethered factory cap. It is powered (12V). I just don't know the purpose if not for accessories.
Which side is your jacket input wired? My wife's Gerbing jacket liner has the connection on the left. I wired the included fused pigtail to the left side, and left my battery tender plug on the right. It only took about 15 minutes.
Only thing i would suggest is making sure it is a fused hot wire so you have a little protection. I used the one supplied with the coat, and its handy to run it up next to the riders backrest, through the seat. tucks out of the way well when not in use....