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SW20 Radiator Fan Control

       Many performing engine swaps will find that the cooling system takes much longer to warm up than a typical front engine car. This is due to the larger coolant capacity of the MR2 and its exposed coolant lines.  In an SW20 the factory radiator fans are not ECU controlled. They are controlled by a temperature switch in the radiator. If the car had A.C., the A.C, amplifier would also be part of this control for highspeed/low speed operation. If you find it necessary to take control of fan operation we will detail how to accomplish this.  At this time I am aware of 2 different factory relay setups controlling the front fans. Cars with factory A.C and cars without. 

           SW20 with factory A.C. 

Option 1. If you want to run fans on full time low speed with key in on position use the picture to the left,  pull 3 relays and jumper pins shown, nothing else necessary. Ignore that blue fuse tap to the left. 


Option 2.  If you want the fans ecu controlled by Kpro. Perform Option 1 first. Then flip box over, pull off lower cover and cut wires to pin 3 , then wire  pin3 to pin 7 at c101 by ecu.

Option3. If you want fans controlled by aftermarket ECU. Perform Option 1 first. Then flip box over, pull off lower cover and cut wires to pin 3 , then wire  pin3 to your fan control wire at ecu. This must be a ground trigger signal.

Note: This wiring will work for any sw20 engine swap. You just need to confirm which pin location on your ecu that controls the fans.

                 SW20 without A.C. 
Thanks to Chris Bailey for supplying the pics and notes for non A.C version.

Same deal as your current instructions: flip the box upside down, remove bottom tray by popping four clips, attach the K-Pro wire from C101 pin #7 (or fan control wire of your ECU) to the ground side of that relay (not the square “Fan Main Relay”.) Tip to novices: the trigger is the smaller gauge wire. Also, I think it makes sense to tap the ground instead of clip it so the stock circuit that runs off the radiator ECT switch is intact — matches Hondata’s swap recommendation as well. (

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