http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1D00YU6RY1DN1C0HZF&year=1987&make=MB&model=300-E-002&category=P&part=Water+Temperature+Sender

http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1D00YU6RY1DN1CEJWY&year=1987&make=MB&model=300-E-002&category=G&part=Engine+Temp.+Sensor



http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1D00YU6RY1DN1C6DSF&year=1987&make=MB&model=300-E-002&category=C&part=Water+Temp.+Sensor&appEngines=_any

Single is temp gauge and 3 prong I already told you..
My schematics verify my info, so either your friend is wrong or Benz schematics are incorrect..