mystery wire on radio connector 96 Passat

96 Passat. I have a wire on the stock stereo connector that I can't find identified anywhere. This is what I've identified so far and how it relates to the Crutchfield connector / adapter for my new head unit install.
VW Red/Brn = new red = 12V ignition switch
VW Grey/Blue = new orange/white = instrument panel dimmer
VW Brown = new black = ground
VW red/white = new yellow = constant 12V
VW no pins = new blue = power antenna that I don't have
VW no pins = new blue jumper = power antenna that I don't have
That all makes sense.
But then I still have a brown/blue on the oem radio and connector. The Crutchfield adapter has two empty holes, one of which aligns with my mystery brown/blue wire. What does the brown/blue wire do? At this point it won't have any connection to the new radio.
Note all of the speaker wires and their various colors are on a different plug.
Thanks in advance for any ideas.

It's probably an alarm sense wire. You can leave it disconnected. Is that pin tied to ground on the original radio?

-J

The B4 Bentley should be able to tell you what it is.

Steve

According to Bentley br/bl, which originally went to radio connector T8a/6 should be ground for left tweeter, and by extension the left front woofer in the driver door.

Steve