how does the gear sensor work?

Meta description: gear selector sensor

….10 yr old thread...Red Bull is having good luck in getting people to respond...
I know I know, I'm sure my gear position indicator is around the same age. I've been needing to redo some wiring and I was on the fence about getting a new GPi. I've seen that the pcv can tune by gear and was entertaining attempting to try to tune by gear and map.