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Tie the white wire on the 86 pin of the relay to the PCM fan signal. That way, both the trinary switch and the PCM control the ground of the relay. You don't need an external temp switch or adjustable thermostat with the PCM.
You could also run two relays in parallel where the 30, 85, and 87 pins on both relays are tied together and the 86 pins have their separate grounding points: one connected to the PCM and the other connected to the trinary switch.
Thank you I thank two relays with separate ground triggers so the pcm doesn’t receive that it’s getting a ground signal when it’s not sending one and turning on the check engine light
I do something very similar on my harnesses. What I do is use the large 30amp relay for the fan or one for each fan and use the trinary switch ground to trigger them. I then use a micro relay off the pcm to trigger the fan relays without throwing a multiple ground code.
Thank you I thank two relays with separate ground triggers so the pcm doesn’t receive that it’s getting a ground signal when it’s not sending one and turning on the check engine light
You could also install a diode on the PCM side, but I agree that two relays in parallel would be better.
You could also install a diode on the PCM side, but I agree that two relays in parallel would be better.
Turning off the code or using relay isolation works best. I've tried a diode and it never worked and after looking over the circuit I don't think it can work.
Thank you everyone I just used one relay for now no codes yet but I haven’t driven it very far yet still working on it.
here is a pic of the car so far
09-25-2018, 11:51 PM
Need help with a vintage air trinity switch wiring 
