The other hard part about the ECU fan signal is getting the AC to work with that properly. The external fan switches address that more easily.
I guess this greatly depends on the ECU. I am very new at this and can easily adjust my temperature and speed of my fans (one or both) relative to the water temp or whether the AC is running from my ECU. I also programmed it to for my AC shut off at certain RPMs and temperature.
Brian Hobaugh SCCA National Tour June 2014
First Hemi 'Cuda Convertible Ever Built
Short clips: Goodguys Pleasanton autocross and pit videos
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