Just curious; why are you interested in pin #85 on the ECM #1 connector. (K157 20BR/OR MASS AIR FLOW 5 VOLT SUPPLY)
Don't see it having anything to do with fans circuit?
Pin #91 on ECM is low speed output ground to the low speed relay.
Pin #71 on ECM is high speed output ground to the low speed relay.
The
key is the fact that the ECM is "Grounding" pins 85 on the control circuit for either the Low Speed Relay or the High Speed Relay to operate the fan in the desired speed. see wiring diagram below.
The ECM is also getting a signal from the AC transductor and exactly how that plays into the whole fan logic is still a mystery.
Without a control logic diagram for the ECM, it is all guesswork.
But if you could find a temperature thermo switch that could ground a relay at a certain desired temperature then you could wire it to one of the fan relays in place of the ECM signal on pin 85.
or
Add a complete separate control circuit using a temperature thermo switch and your own relay to operate a fan at a desired temperature.
But if you go this route, you would need to add a diode to prevent any backfeed I would think unless you totally abandon the ECM feed to the fan relay of your choosing.

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