The NSS appears to have 4 contacts, I'm not sure which ones you would want to jumper:

http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1CQ0J3JZ426A129GTI&year=1981&make=MB&model=300-D-002&category=J&part=Neutral+Safety+Switch