2000 Deville Reverse Lights not working

I have a 2000 Deville with 105K miles, and recently the reverse (back up) lights stopped working. Checked all the wiring, lamps, fuses, etc. and all looks fine.
I replaced the back up lamp relay, and still no good.
Any insights? Could this be related to the park - neutral switch? What about other diagnostics I can perform to narrow this down? Thanks.

PRNDL sensor on the top of the trans where the linkage connects is in the circuit look at that for continuity.

Thanks! I will check it out. Is there a schematic that indicates location?
Do you happen to know the part number if I need to replace the sensor?

PRNDL sensor on the top of the trans where the linkage connects is in the circuit look at that for continuity.