Rewiring Fan relay

Printed From: the12volt.com
Forum Name: Relays
Forum Discription: Relay Diagrams, SPDT Relays, SPST Relays, DPDT Relays, Latching Relays, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=141631
Printed Date: May 13, 2025 at 4:56 AM

Topic: Rewiring Fan relay

Posted By: bosco32
Subject: Rewiring Fan relay
Date Posted: August 22, 2016 at 11:30 AM

Hi all,

I need some assistance please...

This is the factory wiring diagram:

posted_image

From my research, the sub fan only operates when the A/C is on?

Now given I do not have A/C anymore on the car, and the front wiring harness (lights, horn, etc etc) is being remade, I want to rewire it so its just the main fan that comes on automatically... and the sub fan and sub fan relays are removed...

Any thoughts/ideas on how i can achieve this?

Replies:

Posted By: bosco32
Date Posted: August 22, 2016 at 11:31 AM

the car in question is a 2012 Subaru WRX STi.

Posted By: lurch228
Date Posted: August 22, 2016 at 1:43 PM

Based on the diagram (Relay holder F27) and all associated wiring is for AC Turn on of both the main and sub fan. So it can be eliminated as thermostatic control of the main fan is controlled by the relay in the Main Fuse Box. Main fan relay 2 holds negative leg of sub fan at +12v until Main fan relay turns on then sub fan negative leg is ground. And Positive leg of sub fan is switched by ECM control of sub fan relay. If Main fan relay 1 doesn't energize then Main fan relay 2 doesn't energize and keeps Sub fan from turning on due to no ground.

Posted By: bosco32
Date Posted: August 22, 2016 at 6:50 PM

lurch228 wrote:

Based on the diagram (Relay holder F27) and all associated wiring is for AC Turn on of both the main and sub fan. So it can be eliminated as thermostatic control of the main fan is controlled by the relay in the Main Fuse Box. Main fan relay 2 holds negative leg of sub fan at +12v until Main fan relay turns on then sub fan negative leg is ground. And Positive leg of sub fan is switched by ECM control of sub fan relay. If Main fan relay 1 doesn't energize then Main fan relay 2 doesn't energize and keeps Sub fan from turning on due to no ground.

Hiya, thanks for following up, So essentially I can dump Main Fan Relay 2 and Sub Fan relay and just wire the fans directly to Main Fan Relay 1?

Posted By: lurch228
Date Posted: August 22, 2016 at 9:46 PM

You posted that you were removing the sub fan.

bosco32 wrote:

I want to rewire it so its just the main fan that comes on automatically... and the sub fan and sub fan relays are removed...

If this is the case then yes for the main fan only.

Posted By: bosco32
Date Posted: August 23, 2016 at 8:28 AM

would this be correct? :)

posted_image

Posted By: lurch228
Date Posted: August 23, 2016 at 10:37 AM

Yes you have ignition power and ecm ground to energize the relay which connects fam motor to battery positive.