I believe that the cable that comes down from the Nav mount has two connectors coming off it. One plugs into the bike's loom and the other is spare. If that is the one you are seeing then I believe it is an audio output from the Nav which can be used to connect to the speaker system on the RT but is redundant on the GS.
OK... thanks for that. I have asked the question to Vines in Guildford as they currently have my bike. Will let you know what they said.
