Scott is correct, the tube is part of the hose that goes to the interior temp sensor. The sensor is a two-piece device. There is the upper plastic part with the "grill" on top of the dash, and the lower part with a nipple to accept the hose that provides the correct temperature. The two plastic parts snap together, one from top, other from bottom. The actual "thermistor" sensor has a wire going to it, and it comes from the side, not through the hose. There is a small connector on the thermistor. The original Mercedes "hose was made of foam rubber, probably to be insulating. Over time, they all dry out an powder away. I used a piece of clear flexible tubing from Home Depot. One side connects to the black hose you see, the other to the plastic nipple. It's hard to see it from the glove box. Try feeling up there for it.

As far as the alarm "black box". You should see it on top of the duct with two connectors. The number on mine was 126 820 0826 (this was based on notes I wrote last year when I was in there on my 560SL). Not sure what you do to disconnect the system. Good Luck.