Background

I did this with a little bit of a twist-The dual intercooler fans are switched by ignition and are always on when the car is running. The fan ECU is now powered continuously, which allows it to switch the engine lid fan on and off, whenever the temperature in the engine bay exceeds 140 degrees, whether the car is running or not. I can override control of the lid fan and make it run continuously if I need to.

Note: Special thanks to Marc "The Spark" Summers for translating the electrical diagrams in the BGB's into English 8^)



Tools needed: 1/4" Drive with 10mm socket and 3" extension
#2 Philips screwdriver
#0 Slotted screwdriver
Wire stripper/crimper
Soldering Iron and solder
Drop light
Parts needed:
1 30+ amp automotive relay
1 Non-polar Electrolytic capacitor (25V-50V at least 4.7uF)
1 1amp 1000piv rectifier diode
10 feet of 16 gauge wire
15 feet of 12 gauge wire
20 feet of 18 gauge two conductor wire (speaker wire would work here)
SPST switch, either toggle or I used push on/push off.
Electrical tape or heat shrink
plastic wire loom and zip ties
double sided 3M automotive tape
7 ring (crimp on) electrical terminals
4 female (crimp on) spade terminals

First solder the diode and capacitor to the relay using the directions in Marc Summers' write up. Mount your fans as required (I have dual 7.5" intercooler fans and one 10" pusher in the engine lid)

disconnect the ground cable from your battery.

Using a #2 Philips screwdriver, remove the two screws securing the trim panel on the passenger side of the engine lid. You will need a 10mm wrench to remove the bolt that holds the ground wire to this panel. Once you have done this, set the panel aside.

open the #2 fuse block in the engine compartment on the drivers side (US models) You will see a white wire with a red rubber cap over it, pull the cap back and you'll see two 10mm nuts. This is where you will pick up constant 12V for your relay. Attach a ring terminal (each) to a 10 foot, 4 foot, and 1 foot length of your 12 gauge wire and secure them under the nuts. Next run the 10 foot wire out through the bottom of the fuse box and up around the back edge of the engine compartment, by the latch and over to the passenger side rear strut tower. Leave yourself about 6 inches of slack and cut the wire. Attach a spade terminal to this end of the wire.

I also ran a second wire (16 gauge) over from a switched ignition source in the #2 fuseblock. I took the 10mm mounting bolts out of the box and flipped it over which allowed me to splice into one of the wires coming off the EFI fuse. This circuit is only energized when the ignition is in the “run” position. I ran this wire around the back of the engine compartment as well, then tucked both wires inside the plastic loom and zip tied it down.

Look at the fuse block in it's normal orientation. There is a round relay located in the end closest to you, right near the coolant overflow bottle. This is the engine fan relay. Flip the box back over and cut the black wire with orange stripe and the black wire with red stripe that go to this relay (pins 1&4 respectively) leave as much wire attached to the relay pins as possible. Tape or heat shrink the other ends of the wires and tuck them out of the way. Now take your 1 foot section of 12 gauge wire that is attached to 12V and splice it to the ends of the 2 wires you just cut that go to the relay. Solder the splice and either heat shrink or electrical tape it. Run your 4 foot section of 12 gauge out through the bottom of the fuse block and back through the large rubber grommet just below it, into the rear trunk. Replace the #2 fusebox, securing it with the two 10mm bolts.

Open the rear trunk and use your slotted screwdriver to push in the little plastic "buttons" that secure the trunk liner and pull the liner away from the wall of the trunk nearest the engine bay. You will see a silver box about 8" square-this is the Engine Control Unit. Don't touch it :P Just to the right and down of the ECU, you will see a small box about the size of a pack of cigarettes, this is the fan ECU. Unplug the connector from the bottom and cut away the plastic sleeve that covers the wires. You need to cut two more wires here, the black wire with a yellow stripe, and the blue wire with a yellow stripe. Again, leave as much wire as possible on the connector side and tape off the ends of the wires that come out of the wire bundle. Now locate your 12 gauge wire where it comes through the rubber grommet, just to the left and down of the main ECU. Run the wire over and splice it to the two wires at the connector. solder your splice and tape or heat shrink it. Plug the connector back into the fan ECU and replace the trunk liner. This step is done.

Go back over to the passenger side of the engine, where the intercooler is. You now have your constant 12V where you will be mounting the relay. Take a length of wire making sure that it is long enough to reach from the grounding bolt on the strut tower to a spot just above the intercooler and attach a ring terminal to one end and a (female) spade terminal on the other end. Attach a ring terminal to the negative (-) wire on each intercooler fan. Unscrew the bolt on the strut tower that the grounding wire for the little trim panel is attached to and slide the ring terminals over the bolt, then re-secure it. The spade terminal will attach to the ground on the bottom of the relay.

Connect your ground, constant 12V, and the wire you ran over from the EFI fuse to their respective terminals. Attach a (female) spade connector to the + side of your fans, (two wire into one terminal) and that goes on the final terminal of the relay. Mount the relay to the ledge above the intercooler using the double sided tape.

Now what I did was to cut the connector off the OEM fan and solder it onto the wires from the 10" decklid fan. The wire with the red stripe is positive (+) on the OEM fan harness.

Now for your switch: I pulled out one of the blank panels next to the fog lamp switch on the dash and secured my push on/push off switch in it. I then ran my 18 gauge wire from the switch, down through the kick panel, and back along the wiring harness under the doorsill. I removed the interior panel that covers the seat belt retractor and rear speaker, and also the storage box lid. This allowed me to pull up the carpet covering the firewall and run my wire out through the big rubber grommet there. I then ran the wire up to the OEM temperature sensor on the engine lid. Cutting one of the wires going to the temperature sensor, I soldered one of my 18 gauge wires to each end of the cut wire. This allows me to take the temperature sensor in and out of the circuit at will. When the temperature sensor is in the circuit, the engine lid fan only comes on if the engine bay temperature hits 140 degrees or more. With the sensor out of the circuit, the fan stays on all the time.

Replace the body and interior panels, re-attach the ground cable to your battery and you are done.

Disclaimer

What you do to your car is your business and responsibility, not mine.