I have a 1995 W140 S420 with a bad central locking pump (PSE pump), or at
least I think I do.

Symptoms...
1) Everything using vacuum off that pump is dead...door lock, trunk latch,
fuel filler door, etc.
2) HVAC vents seem to go into "fail safe" mode upon acceleration - I've read
where this pump provides extra vacuum for the HVAC system when needed.
3) With rear seat and protective foam box removed, I can hear what sounds
like a relay actuating in the pump...a "solid" click, whenever I think the
pump should be turning on and off.  I do not hear or feel the motor run,
like I can with the closing assist pump under the same circumstances.
4) Just to be thorough, I checked and get no vacuum on any line from the
pump at any time.
5) Yes...I checked the fuses.

Questions...
1) How can I do a bit more incisive debugging ?  I can't make sense of what
alldata.com has.  I would at least like to check supply voltage and a
control signal or something.  Anybody know the pinout on the pump?
2) Assuming I have to buy a new one, I checked and found it offered on at
least 8 different websites.  I found a high of $569.20, 5 at $485.6, 2
others in the $400's, and one at $292.00!  My unit matches both the Bosch
and MB parts numbers of all the websites.  I'd obviously like the one at
$292.00 but I'm wondering what I'm missing if everyone else wants 200 bucks
more.  The site is www.autohausaz.com.  Anyone have any opinions on them?  I
haven't seen anything on any of the sites (remanufactured vs. new, etc.)
that seems to explain the big difference.
3) I seem to remember one site mentioning that a replacement pump may have
to be reset by the dealer.  Anyone know anything about this?

Notes...
I took the pump out in order to try to play with it and maybe rebuild it (a
la the duovalve rebuild of Pete at
http://v12uberalles.com/Rear_AC_System.htm ...that saved me $500...thanks
Pete).  However, I discovered the car will not start unless the pump is
hooked up.  I got lazy and pissed and just hooked the whole thing back up
and didn't bother to check what part of the hook up controlled that.

Anyway...thanks in advance for any help...John