On the 126, can you pull the fuse for the AUX water pump instead of unplugging it? May be easier if the wires are buried. May also disable other components too though. If they are Climate Control related components, this may or may not confuse this as a t-shoot step.
Pump is expensive, yes, but all in all, $100 to $140 is not bad for an electric hot h2o pump which has lasted me (eruh, the car -- I bought it used) 167k miles and 17 years.
1986 300E Anthracite + ECodes + MB Mileage Award