The 1971 Chrysler Imperial Autotemp 2 Service Reference Guide indicates an Auto-Temp 2 Tester is available (Chrysler only? but the 10-pin test plug is accessable on my system at the lower right passenger footwell so I'm assuming this works for the MB as well)

Here is what it says:

The Auto-Temp II Tester is essentially a resistence substitution device which bypasses the sensors and selector dial to control the system manually. By switching in present resistance values, you can check the system operation completely, regardless of the surrounding temperature.


Sounds perfect to me.

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2009 R350, now the daily driver
1980 300SD, was the daily driver