Trinary and 3 relay electric fan questions

[SilverGT3RS]

Hey everyone-

I’ve been searching around trying to find an answer for adding AC to my LS swap-lots of info floating around, but also a lot of conflicting info. To add to the confusion theres a lot of info that’s 10 years old.

First an overview of my setup. 2004 6.0 LQ9 out of a Cadillac Escalade. Using factory PCM and main wire harness, DBW. I have HP Tuners. Engine and trans swapped over into a 67 C10, using aftermarket radiator with 2 electric fans with 3 relay harness -using green and blue wire to drive fans via the ECU similar to the schematic below.







I’m adding a Classic Air system, and from what I’ve read using the trinary switch is the simplistic way to go.

My confusion comes from some guys saying you need a diode wired inline if you hook the blue trinary wire to the fan relay to keep from throwing the check engine light.


Others show using a small separate relay. Problem there is I couldn’t find any info on relay size. I’m assuming it would need to be 30-40 amps? I’m also assuming I’d need a busbar of some kind?



What’s the easiest way to accomplish turning on the fans when using the AC with my setup?
Should I be exploring anything outside of the trinary switch?

Thanks in advance!