Z1OwnersClub GB

Not a Zed question so apologies.
My brother has sadly passed away and I'm preparing to sell his GSX650F.
Can anybody tell me what the aftermarket switch in the middle of the photo is for?
It's got three positions (off/start/on) as you can see but even in the "off" position the bike starts, runs and rides fine.
I've never had a bike newer than 1979 so I didn't want to switch it without some clue to what it might do.

It could be a switch for heated grips?

Heated seat, though the handlebar grips aren't standard so as JB says possibly heated grips. Unless the switch is actually from something else that he used I can't think of anything it could be for. Possibly a kill switch but as you say it still runs. Only way to find out is to turn it.
And sorry for your loss.

Pretty sure its a heated grip controller.

Thanks everyone for the replies.
It turns out that it is indeed the on/off switch for heated grips.
Silly me