extra vacuum line (84 5kS) + sparkplugs

["G. Benedikt Rochow" <rochow@segosf.hlo.dec.com>]

Doing a general survey for more broken or
unplugged stuff in my 'new' '84 5000S
(just how old would a Bosch sparkplug have to
be before the contact piece at the end rips
off and stays in the plug wire when pulling off
the latter? :), 
I found what seems to be a rubber vaccum hose, hanging 
around unattached. More precisely, a hose comes from under 
the top edge of the left outer fender and goes immediately 
under the coolant reservoir, towards the brake fluid reservoir,
and into a T connector there. It continues straight to
what seems to be a vacuum actuator, that would pull
a metal arm that (I'm guessing here) apparently turns
the throttle (That has another arm that RubeGoldbergs 
to the pedal area). I get the general impression that it's 
cruise-control stuff; my c-c doesn't work, which fits (but many
other things don't work either, so that may not mean much.)

But the side port of the T connector has a less than 30cm piece
of hose with a short straight connector at the end, which is just
dangling. What is it? What should I do with it?

different topic:
When changing spark plugs, is there anything bizarre (besides
the way this car has been neglected) that I should watch out for?

TIA.

-G. Benedikt Rochow