Triggering the Fan Relays

[Wagon Master]

For my LS1 swap I used the Painless harness for the engine and the computer. I worked out great. But the one thing I'm confused about is the two fan wires that come from the computer out of the harness that energizes the two fan relays. I was told by Painless that these wires will go ground when the engine temp reaches the trigger point. So I would have to put a constant (battery) 12v on one side of the relay coil and the trigger wire on the other.

Has anyone else had any experience with the Painless harness and is what they are telling me the truth? I thought it would be the other way around, that I would ground one side of the relay coil and connect the fan wire from the harness to the other side and that would feed the 12v to trigger the relay.

I'm looking for some consensus so I don't wire it the wrong way and damage the computer.

Thanks!

 

[lt4malibu]

the wires should be blue and green, the ecm grounds the relays depending on what speed.

 

[Wagon Master]

Yes, they are blue and green (and labeled), and thanks for the confirmation that the computer does take it to ground.

 

[Wagon Master]

Ok...now your schematic opens up another question. There are two ECM triggers and two fans. Originally I was going to wire each ECM trigger to it's own relay and fan. Now I see from the schematic that there are three relays. Should I duplicate the schematic to wire my fans with the three relays or is it OK to go with my original plan of one trigger and relay per fan?

From the schematic it looks like when the low speed is triggered, both fans are on and they in series (runs slower) and when the high speed is triggered, both fans are on and they are in parallel (runs faster). Correct?

 

[lt4malibu]

i always run the 3 relays so the ECM can command 3 speeds for the fan

 

[Wagon Master]

Thanks, I ordered the Painless dual fan relay kit, 30118. Looks like it has every thing I need and then some (I won't need the temp sensors).