The switch is located just behind the gear selector cable termination where it clips onto the the selector shaft. See just beyond it a strange shaped diecast ally and plastic device - that's it.
Follow its lead up the clean its connector too.
Also, always worth cleaning the ECU connector at the ECU end too. The ECU is in a very hostile place under the battery tray. To get at it you need to remove the battery tray and that means removing the air box again!
Oh, and don't forget to disconnect the battery first
