I have a question. Do those switches wear out over time without going out completely? On my Jimmy and Caprice, you have to put the lever in just the right position or the lights won't come on. Or is it adjustable?
At one point a few years ago I was having the same trouble keeping the back-up lights on as you. Most of the time it wasn't really an issue.
But it does become an issue when - in order to keep the back-up lights illuminated - you have to keep upward pressure on the shift lever with your right hand while trying to back down a steep dark driveway in the middle of the woods with just your left hand.
Just so happens that I have a steep dark driveway in the middle of the woods. So one day I decided to at least look at the switch. Often that's as far as I get.
This time however, I fixed it. Took about 2 minutes and zero dollars.
While I was poking at one side of the switch with my finger, the entire assembly made a ratcheting sound and rotated around the steering column. Seems that the plastic housing (which sets the open/close point for the contacts within) is infinitely adjustable.
It might take a few minutes to dial it in, but it is time well spent. Basically, the procedure goes like this: put your gear shift in R and then (with the key on) have someone watch the back-up lights. Push the switch one way or the other - I forget - until the back-ups come on.