I responded via PM since I check those first, but here's an article I wrote up when my backup lights didn't light on known good bulbs:
http://www.peachparts.com/Wikka/W108NeutralSafetySwitch

Mine just needed a good cleaning.

__________________
Current:
2021 Charger Scat Pack Widebody "Sinabee"
2018 Durango R/T

Previous:
1972 280SE 4.5
2014 Jeep Grand Cherokee Limited "Hefe", 1992 Jeep Cherokee Laredo "Jeepy", 2006 Charger R/T "Hemi"
1999 Chrysler 300M - RIP @ 221k