If it is a second connector on the cable that goes to the satnav, then it is the audio output from the Nav, and is used on bikes with an audio system like the RT. On the GS it is redundant and usually has a dummy connector on it to protect the pins.
I tapped into this to fit an audio jack socket when I was experimenting with outputting the audio from the Nav into an additional BlueTooth transmitter so my wife could hear the audio instructions at the same time as me. However I never got round to fully trying this, but I think the reason was that while transmitting to the rider via Bluetooth, I found that the Nav did not output any audio on this connection, though when I turned Bluetooth off and plugged some headphones into this output I could hear the instructions. Maybe I missed some setting which would have allowed it to output audio from both, but irrelevant now as I don't use the Nav anymore.
If it is for a non-fitted charcoal canister then I've not seen it floating around on my 2017 bike - must have a look! I wonder if it could be used as a power source?