Backup light / 1-4 issue

[Matt B]

One my bumpy road to get my Z road legal there is one last open issue - as far as I can oversee at the moment. My backup lights don't work. Neither does the 1-4 upshift function - which seems to be an advantage but may indicate a "deeper" issue...
Here's my analysis results:

- Connector 237, R/H under dash, blue wire on pin "N": being the power source for B/U and 1-4 it reads 12.8V with ignition on
- Connector 239, R/H under dash, light green wire on pin "D", coming from the B/U switch: the incoming wire should read around 12V with ignition on and reverse gear engage but doesn't. Reading is 0. Outgoing side proves grounded via the backup bulbs as expected.
- To verify that there is no issue around splice S118 (which I couldn't locate) I tested voltage at 1-4 upshift solenoid connector. With ignition on but engine off it reads about 10V green/white wire vs. black wire as well as versus ground. So the dark blue wire routing current into the upshift relay (same as routes current to the backup light switch) must be hot as expected.
- bridging the C237 N and 239 D (and thereby simulating a closed B/U switch) turns on the backup light as it should

So, to me it seems very obvious that the backup light switch has an issue, however I didn't find a way to pull it with the tranny in place.
What concerns me is that the 1-4 upshift is inactive, too though there is voltage applied. I.e. I can shift through all gears with no effort, no matter if the engine is running or not. Coincidence? Both devices defect? Or does it indicate a deeper issue?

Unfortunately the backup light switch is in such a poor position that I don't see a chance to directly analyze its behavior at the pins. And before I try to pull it (which seems awkward) I want to make sure I didn't oversee anything.