Yep, the system as described in the 1996 schematic makes sense... the 1997 system looks overly complicated just to tell you the coolant is low... there must be a reason, but not apparent to me.
Anyway, sorry this process took so long, but lots of knowledge gained... will have to check my '96 and see how its wired... :-)
Glad information helped.

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KenP

1996 S500 W140 Coupe