ON the 04 and older bikes the gear indicator had to be plugged into the wiring harness that comes from the gear position switch under the airbox. On the 04 and older bike with ABS, you couldn't reach this connector from the front because of the ABS plumbing and extra stuff in the way. On the non ABS 04 and older, you could reach the connection thru the front by removing some of the front fairing pieces.
On the 05 and later bikes, the gear indicator plugs into the ECM's service connector and reads data from the ECM to determine which gear it's in. The older bikes ECM wasn't capable of this function thru their service connector.