Thanks for the pic. That makes sense now. My PT has a single sensor installed there already, which is apparently part of the engine control system. The console sensor appears to be completely separate, and gets wired directly back to the console connector.
It looks as if the engine sensor and the console sensor are the same type? I found an online source selling an aftermarket replacement sensor here:
RockAuto Parts Catalog
This *LOOKS* like the items in the drawing, and like the one already under my hood.
I still would like to find details for the headliner opening before I start cutting blindly.