I think this socket is not there.
I was trying to think across the devices in this area, but it does not hold, really:
- washer pump - other side of fire wall
- kick-down switch - other side of firewall
- trouble light socket - does not have this type of connector, I think
- I thought heated rear window - but original installation (yes, it goes that way) does not have this connector in that place, there is just connector in B-pillar
Maybe somebody just connected some accessory there? Additional switch?