V8 cruise control

[FBFISH@aol.com]

Gentlemen-I would like to trouble shoot/repair the cruise control on my 1990
V8. The documentation I have shows there are four parts involved:
       * switch (on steering column)
       * control unit (behind dash on passenger side)
       * vacuum control motor
       * vacuum vent valve brake switch
The dealer said that the control unit is bad, but he hasn't been correct
about anything yet so I don't want to spring for a new control unit until its
been properly isolated.
    Questions:
       1. Where is the vacuum control unit located?
       2. Where is thevacuum vent valve located?
       3. Can I access the control unit without removing the 
           top of the dash ie fron under or thru glove box?
Your wisdom will be appreciated.TIA and MERRY CHRISTMAS!!!