So...I'm not using the 3 relay setup that came stock for an ls1, but instead 2 relays. They're hooked up dead simple, such that when the pcm grounds fan #1, it turns on. Same for fan #2. What has me puzzled is that one of the fans runs as soon as the key is turned on (before crank even). The second fan turns on after 100 degrees is reached. This can't be normal... Below is the stock ls1 fan configuration with 3 relays. Will wiring it up like this get me "normal" fan operation (no fan turned on before crank)? What is everybody else doing for fan controls? I'm past the point of getting the relay center used... I'll just wire it up if need be. Thanks fellas!

hmmm..... that's weird that the pcm is grounding the cooling fan relay number 1 upon ignition. Just curious, when you had your pcm tuned what were the fan temp parameters set at?

I am running all 3 relays now. I did have just the two, but had issues with it

-jason

What issues did you have?

I'm not sure what the fan temp parameters were set to...my tuners left a bit to be desired. I'll be checking the connection at the pcm this Friday to see if it is in fact doing the grounding, or if maybe I have a short somewhere. It's a bundled Speartech harness, so I somewhat doubt the short.

if they are hooked to the correct terminals on the pcm they will not turn on with ignition. whether you are using two or three relays. the turn on and off temps need to be set with a tune.

i went with aftermarket controller, less wires to run and simpler.
Attached is the diagram that i was using but it also shows 3 relays for the fans
edit: removed the diagram to use in a different thread

i do all my ls1 swaps with just 2 fan relays. The ls1 stock fan setup on an f-body is designed to run 1 fan at low speed. then when the second fan kicks in it will run both fans at high speed.

Running 2 relays works just fine. you only have a high speed on your fans but its no big deal. pcm controls your fans through grounding the relays. i used 2 of the stock relays in teh stock locations on my 92 for my fans, worked great

So it sounds like I may have a wiring issue, bad relay, or the pcm is set too low for fan #1. I'll post some test results come this weekend. Thanks fellas!