Ultimate Fan-switch Mod!
x3ro : pics, main write-up, instructions

BETTER Install Instructions for a better cooling fan mod!

(This mod was done on a 4th Gen OBD-II vehicle, but can also be done on a OBD-I vehicle as well, BUT wiring the hot 12v+ wire for the LED's should be done differently, here's why: I would also suggest using a switched power source for the LEDs on the OBD-I cars. One or both LEDs (depending on whether you have a 2 or 3 relay system) may remain ON when the key is off. The control side of the OBD-I fan relays have +12v supplied to them only when the key is ON. Therefore you cannot run the fans unless the key is on anyway. The OBD-II cars have +12v powered to the control side of the fan relays all the time. The LEDs do not exhibit the same behavior as above. Therefore, you can use an always hot feed for the LEDs like the cigarette lighter and you will be able to turn your fans ON with the key off. This is why some people complain of the LEDs staying on on their OBD-I car when they have followed the instructions that were made by someone with an OBD-II car (like the popular "shanemar" page). Just be aware of the differences.) So, if you have an OBD-I car, be SURE to use a switched 12v+ power source, these are power sources that only recieve 12v+ when the ignition position is "on" or "run" or the vehicle is running!

Remember, do not start the car with the fans already running, or you WILL set a SES light..This mod will NOT interfere with stock PCM operation of the fans, so if the switch is off, they will operate as if there was no modification to them.......Also, SOLDER AND TAPE ALL CONNECTIONS!

Materials needed (everything can be found at Radio Shack):

(1) DPDT switch, make sure its ON-OFF-ON (center off switch)

(2) LEDs, your choice of sizes and colors, 2-2.1v range

(2) 470-ohm 1/2w resistors, 5% tolerance

Lengths of wire (your choice of color, as long as you remember what color is for what =] )

Male and female quick-disconnects


Good quality electrical tape (black or colored, your choice)

Don't forget your tools! (Soldering iron, wire cutter/stripper/crimper, Dremel or other tool you can use for drilling and widening a hole)


Lets keep movin' fella's, now that we have all our materials, lets get started (but first, remove your battery + wire!!!!)

I didn't take pics of the first few steps, but they're very simple (I'll take pics later if I get a chance) ((This only applies to '97+ Consoles, I'm unsure of earlier years! Removal of the upper console is for M6, I dont know how to do this on an A4! Sorry.))

1. Open your storage part of the console, take out your coin holder (if applicable), there will be two 7MM bolts, remove them. Also, remove your shift knob and your shift boot....Next, grasp the cupholder part of the upper console (the part w/ the single cup holder, and where your shifter (This mostly applies to the M6, I'm unsure as how you'd do this in an A4) is, pull backwards slowly, and the upper console will pop off, be sure to disconnect the cigarrete lighter plug......This is the part you will drill the holes for the LEDs and Switch in (if you choose to, you can mount the LED's and switch anywhere you want, but this looks cool =] )........

2. Next you'll drill the holes in your upper console. Mark the holes with a marker of some sort, make sure you leave room for the switch on either side for the LED's to mount next to. If you put them too close to the back of the switch, it won't fit right, I learned the hard way =\ Using a Dremel (this is what I used), pick a small drill bit, on about 1k RPM (for the folks w/ the variable speed Dremel), drill the hole for your switch. Yes, I know the hole is too small for the switch right now =] Turn your Dremel back on 1k RPM, and slowly work around the hole, enlarging it with the drill bit...Make the hole just big enough to squeeze the switch in..Now do the same thing for the LED's! Clean up the console, getting all the little plastic peices and stuff off, and clean up the holes a bit, and set that peice aside.

3. Now comes the fun part, WIRING THE SWITCH!!!! YAY!! =] Please make sure to solder all connections at the switch, and tape them up afterwards so there's no chance of shorts! We'll start with an easy to understand diagram of the basic wiring on the switch:

This diagram was done in AutoCAD, btw =] Go me, go me ;] Anyways, it's pretty basic stuff...The only part that may be tricky to some are the grounds...The ground is basically daisy-chained from the right bottom pole to the two left uppper and lower poles...The rest is pretty self-explanitory, any questions, feel free to EMAIL ME ....When I first looked at the diagram, I was pretty confused on how this whole thing worked, but I got some free time and sat down and figured it out, here are a couple diagrams to show you how they work (be sure to check them out): FANS OFF DIAGRAM , LOW SPEED DIAGRAM and the HIGH SPEED DIAGRAM .............

3. Alrighty, now that we have the switch and leds all wired up and ready to go, there should be four wires that are not connected to anything hanging from the mass of switch, wire and LED's...There should be one Ground wire, one 12V+ wire (from the led/resistor setup), one wire that will go to the Dark Green wire, and one wire that will go to the Dark Blue wire..

4. Now we need to go under the hood =] Go ahead and heat up your soldering gun again....Next, go to the passenger side fender of the car, you'll see THREE sets of large connectors right inside on the upper part of the tire hump HERE'S A PIC OF ALL THREE CONNECTORS ...We'll be working with the foremost connector...Now put on your magnifying glasses and look at the connector, for each wire, there's a raise letter..Look for a blue and a green wire, the blue wire will have the raised letter H, and the green wire will have the raised letter J..

Here's what to do with the wires and how to splice into them:

Be sure to tape up all wiring securely once you're finished soldering =]

5. Now go ahead and run the wires into the car somehow; I ran mine down the side of the fender, and through the door opening, its not very noticable when you open the door.....Also run the wires under the panel under the Glove box..And figure out a way to fish them in and under the console till the reach near the cigarette lighter plug...I used the cigarette lighter + and - for my connections, they're the easiest to reach, and the safest to use...

6. I cut the orange (12v+) wire from the cig. lighter, and then stripped the two ends, i then twisted the wires together, and put then twisted ends into a female quick disconnect and crimped it on real well....Do the same for the ground wire...I then crimped male quick disconnects onto the 12v+ and ground wires from the switch/led assembly.......For the green and blue wires from the switch led assembly i used female quick disconnects, and then on the blue and green wires from under the hood, i used the male quick disconnects....That way, you cant accidently connect things backwards...

7. Before you mount your switch and LED's, wire everything up and reconnect the battery + wire, test the switch.....Make note of which LED lights up when you flip the switch to the low speed setting, this LED should be on the left when you mount it to the console.....Make sure you mount it so when you flip the switch to the left, the led LED lights up....When you flip it to the right, BOTH LED's should light up, this is the high speed fans....

8. Now's the time to go ahead and mount your leds and switch to the upper console you drilled holes in earlier..The actuall switch should have a nut on it....You'll slide the switch through, then tighten down the nut...Now for the LEDs, you can use whatever you want.....Be creative =]

9. Go ahead and reinstall the upper console in the opposite way as you removed it, and put everything back together, that's it!!!!! We're done!!!! WOHOOOOO!!

Here are some pics of my setup:

Fans off/stock PCM operation of the fans:

Fans on low speed:

Fans on high speed:

This was submitted to and by user x3ro