Bad backup light switch?

You don't necessarily have to drain all the fluid to change it. I swapped mine out because the old one was leaking and I just backed the car into the driveway (slight incline down on the nose), then jacked the back end way up to try to get as much fluid forward as I could. Then I just made sure I had the other switch in hand when I pulled the old one out. Didn't lose much fluid at all, but it's potentially a little messy.