I believe he (she)'s referring to an automatic transmission, as the manual doesn't have a gear identification sensor or switch.
The only wiring, switches or sensors on this trans is the single, mechanically activated reverse lamp switch. It's almost identical to the one on my '69 2002: just a push button switch that is "pushed" by the reverse selector rod inside the trans and opens or closes a circuit. Disconnecting this switch would have the same effect as being out of reverse, as the circuit would be open. As previously mentioned, this has no effect, so I'm thinking it's a lighting module.
Thanks for the interest and the search though! Keep coming with more ideas!
Jono