PWM cooling fan(s) control using ECM

[Old66Tiger]

Good thread. I have a few questions...

I am running an E38 ECU and currently have it set up in discrete mode with a pair of spal fans. I understand that programming is required to switch to PWM mode. I also understand that a binary or trinary switch is required to control the vintage air compressor for over or under pressure conditions. My question surrounds the need for a high pressure signal from the a.c. system to kick the fans into high speed. Is it possible to let the trinary switch send a ground signal to the ECU to send the fans to high speed when the a.c. system requires it? I have an a.c. input from the speartech harness for an a.c. input. Otherwise I will need to wire in a second switch into the #6 line between the condenser and the evap.