Extra bulb socket in each tail light

When changing the bulbs in the tail lights on my '00 Golf I noticed there was an extra bulb socket on each light assembly. It's on the bottom farthest away from the center on each assembly. The rear light housing has a piece of plastic blocking a bulb from being pushed in and consequently from being put in the associated bulb socket.

Why is there this extra bulb socket and what are the details for it?

its for rear foglamps....many threads cover this

You can add bulbs and have extra brake lights. I took a Dremel tool and cut out the plastic that was blocking access to one of the bulbs.

Check out the "5 brake light" mod. I believe it is in the How-To section. It took me about 10 minutes to do and cost about $8.00.