Can anyone explain the lower 'tailgate closed' sensor?

[Motomixr]

08 X5, the upper gate/trunk door is operating intermittently, sometimes opening/closing, sometimes not. The lock release always works.

I know the lower tailgate has to be forcefully closed, but the intermittent thing has popped up recently.

Troubleshooting, I'd like to be able to check this switch (or sensor, or circuit, or whatever it is) to make sure it's working, not blocked, aligned, or whatever.

TerminatorX5 had a great post in which it is described as the "Micro-switch, lower luggage compartment lid", but where is it? Is it an actual physical switch?

Thanks -