And let's not overlook the infamous OVP - over voltage protection relay. I had a somewhat similar situation a few yrs. back that was cured by a new OVP.

http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=24S1DLNMJ25711GAH0&year=1987&make=MB&model=420-SEL-001&category=P&part=Overload+Relay

__________________
Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"