Official Electric Fan wiring thread!

[Austrianvespaguy]

If any of you like me want to control your electric fan from an aftermarket ECU (such as Megasquirt) that only has ground-switched outputs, I've figured out a great way to rewire things to accomplish this! While the original method works OK to control it with the temperature switch in the radiator, I’ve never loved this solution. It comes on at a bit higher temperature than I’d like, plus I always prefer basing control off of engine coolant temperature rather than radiator coolant temperature. Since the factory electrical system already HAS two different fan relays (high and normal speed), and my MSPNPPro ECU has plenty of spare outputs, I figured this was a worthy upgrade. Here’s the caveat though: the factory wiring is all set up for high-side (12v) control, while basically all standard ECU outputs are low-side (ground) switched. Fortunately, I found at great way to work around this issue while – as always – preserving as much of the factory wiring as possible in order to keep such modifications reversible. So here goes, first the schematic of what we need to accomplish:

What we’re doing here is leaving the ‘Normal Speed’ circuit alone so that it will STILL turn the fan on should either the radiator temperature get hot enough OR if the AC is switched on. We will instead just hijack the ‘High Speed’ relay to actuate based on the ECU ground-switch control. The first step is to simply bypass the higher temperature switch by connecting the Black/Brown wire from terminal 3 directly to the Green/Black wire at terminal 1 so that the relay now always has +12v from Fuse 19.

If we stop here the relay will be constantly energized and the fan will just run all the time, so the next step is to remove its factory ground connection, and run a new wire to the ECU output which will instead control when it is grounded. To do this you need to remove the upper half of the fuse box. The top half is held down with 3 small screws (circled in red), one on the exterior outboard (drivers fender) side, one just above Fuse #2, and the final one underneath the fog light relay K8:

With those out you can then lift the top of the fuse box up enough to access the wiring on the underside. You’ll need to use a small jeweler’s screwdriver to bend the locking tab of the relay coil’s ground side connector inward (yellow arrow) so that you can remove the spade terminal out the bottom. Once it’s out, insulate it so that it doesn’t touch/ground out anything else in there, and then shove a NEW wire (with a similar tabbed spade terminal) in there instead. This is your new control wire that you then just need to run out through the fuse box and to your desired ECU output:

And now just enjoy your new programmable/ECU controlled cooling!

[carguy101]

Saving this for later. Thanks!

[EbzyyE30]

Hello this is an older thread but maybe someone will see it and be able to help me out. I have followed all the steps to get my fan to work and there is no luck whatsoever. I have an s52 e30 1989 so late model with the AC fan plug under the drivers side headlight. I get power to the green/black wire to the fan switch, no power to the black/brown and when I tie them together I should get power to the brown ground wire in the fan plug on the chassis and that is the case I get 12v with key ON, but my problem is I do not get power to the blue wire when the fan switch wires are shorted together. I checked my relays and swapped them around with one another and unless all my relays are kaput I have no idea what’s going on. To my knowledge I have good ground and the fan does work when I plug it in directly to the battery. I’m not sure if it matters but the ECU and engine harness are not hooked up so maybe that is my issue but again I’m not sure.

[jbontke]

https://youtu.be/4w_8SvET7wM?t=27

Run a fused power wire (power applied when ign switch is on) to 85. Then run the ground wire from 86 to your switch (other wire of switch just runs to chassis ground). That way your switch is grounding the replay and you dont have long runs of 12v + power wire.

[thankyoubasedjosh]

Chiming in here with my modified electric fan setup.

Short story: I followed this DIY on how hook directly to the Aux fan wiring with a 80C switch. Easy to do, simple and not a lot of electrical cabling. I was running a SPAL 16'' Puller as my primary cooling fan for a few months.

This worked like a charm- except under the ONE scenario: If the temp switch kicks on the fan at 80C and starts cooling, and I was ready to park or turn off the car and the fan was still on- the fan would obviously lose power. IF I had to turn the car back on for whatever reason (maybe to move the car after you parked it) and the temp was still over 80C- the startup of the ignition I would blow the stock 30A aux fan fuse every time. I found out that this can happen when switching from the +12v of the battery (ignition ON but engine OFF) to the new +14.3v you get from turning over the engine and obtaining the power bump from running from the Alternator. By the way- I never blew the in-line fuse I added from the +12v of the fan- only the 30A fuse in the fusebox.

Also- which is a great point on why I modified it- was that say you are getting ready to pull into your destination, you might be idling a bit to find parking etc etc and the car gets up to 80C. The fan kicks on and might still be running when you turn the car off. Which is fine. But if you need to turn the car back on again, the thermo switch on the thermostat- which goes to the DME- will tell the DME that the engine coolant is too hot and don't supply fuel. So you get this hesitation when trying to start up. I can't get a definite temperature of what the thermostat DME switch reads that tells the engine that it is too hot. I only found out what resistance it reads at certain temps. If you know- I would really be interested what this threshold is.

Anyway- my plan was to remove the fan from the Aux wiring fuses/relay and run power directly to a new relay that has constant +12v w/o the ignition on. First tried to wire up a new relay and fuse to the stock fusebox. Wasted my time since I couldn't find the correct female blade inserts for the fusebox. Decided to do a completely standalone setup.

Here is what I used and how I wired it in:

Hella 30A Relay and weather proof wiring harness $15
- Relays are pretty much all the same from what I found. Went with this one since I decided on mounting it stand-alone from everything else and tried to make the install clean. Sure you can use a standard Autozone 30A relay, but finding the wiring harnesses are hard to find locally and at the end it will probably be a pretty messy wiring job. Installed mine on the side of the fuel pump relay cover.

30A In-Line fuse holders $4/each
- Used this instead of using the Accessory fuse holder (some have used this stock fuse holder for other things) Put one from the +12v Constant coming out of this stock fuse holder to terminal 30 on the relay. Used the other one for the +12v for the fan.

Here is my drawing and relay layout.

Relay Wiring
Terminal 30: +12v (12GA wire) constant from stock accessory fusebox (with In-line 30A fuse)
Terminal 85: Ground (12GA wire)
Terminal 86: Trigger switch (14/16GA wire) I'm using my 80C thermo switch with a manual override switch that I used a extra fog light switch and mounted it next to the defrost/hazards (to turn on the fan under 80C if needed) You need to tap into a 7.5 fuse that has constant +12v so fuses 21, 22 and 23 are always on. I tapped fuse 21 (NOT 10 as pictured) since it is used for other switches on the car. Run a wire from here, to the thermo switch. Then a second wire back to Terminal 86.
Terminal 87: Fan +12v (12GA wire) used an in-line fuse here to protect the fan. Mounted it near the fusebox for easy access.
Terminal 87A: NOT USED (unless you need power to something that is ALWAYS on and OFF when the fan is ON)

Notes:
Make sure you invest in good butt connectors, crimp (or solder if you prefer) and electrical wrap. I hate glossy electrical tape, so I purchased some premium wire wrap.

Thats about it! It's not the most complex job, but it gets it done and doesn't rely on anything stock. Hopefully this will help out people who might see the same issues. There are a few threads around that I've read about their fans blowing fuses left and right. This should be the solution. Good luck!!

Hate to bring up an old thread but I am following this guide, I have wired up everything according to the drawing, 85 grounded to the chassis, 30 to the auxiliary fuse box constant with an in line fuse, 87 to the spal fan (spal fan also grounded to chassis), but I am having issues since I want to wire it only to a rocker switch. I have a 2 prong switch, I am wiring one side of the switch to the auxiliary fuse box for power and the other end to 86. What am I doing wrong? I only want to wire it to the 2 prong rocker.

[jjc034]

Ok! So for those who are still confused about the setup (which after reading over the many pages of posts, there seems to be quite a few) I have some clear answers and pictures for you. First off, explaining the system (at least on a late-model '89 like mine): - Thermo switch on right side of radiator: 3-prong switch that triggers low speed/ high speed operation of fan. Green/ black is common wire, then black/ brown triggers high-speed relay & black triggers low-speed relay. The different speeds are triggered once coolant in radiator reaches a certain temp. Low-speed at lower temp trigger, high- speed at higher temp trigger - Wiring runs from thermoswitch, across front bumper behind grill, and makes a Y by the driver's side headlight. - Thermo switch wiring runs to relays, then comes back to driver's headlight and goes to aux fan - On my car, aux fan was removed for intercooler and wires were already cut, but here is what I looked at (and you should see similar) - Aux fan wiring: brown = ground, red = switched 12v coming on with high speed, 2 x black wires = one is triggered by low speed and the other high speed. You'll need to test which one is which. - Mine didn't still have the relay on low-speed side, but essentially to deliver a slower fan speed when the black wire at thermo switch is tripped, a 0.6ohm resistor is used in line with low-speed black wire on aux fan side SO now that you understand the basic path of everything, onto wiring: - thermoswitch wiring untouched (I am debating on keeping 3 prong or moving to 2 prong) - aux fan ground to electric fan ground - aux fan high speed red and black wires combined - aux fan high speed and low speed wires combined (remember if you want to maintain low speed functionality, you need to have 0.6ohm resistor on low line before combining with high speed) - all aux fan 12v wires go into inline 25A fuse (likely overkill since current is already traveling through stock fuse box) - inline fuse to fan wiring Now some of you may ask why I didn't just combine all three speed wires together. Well, I will eventually add resistor and am going to test system with 2 prong low temp and 3 prong to see if there's any difference. Also just easier for me to remember what's going on. With all that wired up, you should now have a fan that doesn't turn on when car is started, turns on when coolant reaches trigger temp, and I guess I'll soon find out if it turns off when ignition is switched and coolant is at trigger temp. Hope this helps. If the system doesn't turn off when I turn off ignition, I will then have to wire through relay that is activated with ignition. Thanks, John Sent from my SM-G973U using Tapatalk

[jjc034]

i've read through this and of course i am also confused. it seems there are different applications for different e30's. i couldnt figure it out so i currently dont have the pigtail plugged into the temp switch on the side of the radiator, and my resistor broke so i have it bypassed and all 3 wires at the bottom my aux fan in my front bumper are connected to each other. fuse #3 has 30A blade in it. the aux fan turns on when i press the snowflake button. i have a 1991 318i. i am looking at the switch on the passenger side of the radiator. the plug had 3 wires going to it 1 top, 1 left and 1 right. The connector was so brittle it cracked and exposed the wires as black, black/brown and black/green. i am assuming it is for ground, low speed and high speed but i do not know which wire is what and where on the plug it goes to. it doesn't seem to match up with the colors people are mentioning here. once i figure out the 3 wires and their orientation to the plug, i can slide them on to the right post in the plug, or buy a new pigtail connector and it should be all good according to factory. i did see a post here that said: black/brown to green/black is high speed, black to green/black is low speed. These match the color wiring i have so does that make the green/black the ground? i bought a new resistor, so when its mounted in, do i connect the 2 smaller wires on the right post and the 1 thicker wire on the left post? or does it even matter as long as two thin wires are together and separate from the thicker wire?

I know this is way old, but same thing happened to me today lol. Damn BMW plastic bits crumbling in your hand.... But yes, to make things universal, BMW uses black/green to mark ground vs brown... no clue why. If you touch the other two wires while keeping one end grounded, you'll hear a clicking. My assumption is the louder click is high speed. Sent from my SM-G973U using Tapatalk

[Flipp]

Hey Everyone!

I just overhauled my cooling bits in my 88 325is. I installed a new Z3m Rad, Spal fan, new hoses, thermostat, and new expansion tank setup. I have A/c and would like the Spal fan to work as stock. I also installed a Mishimoto Fan controller kit and have everything wired up and routed where I'd like it to be. one question I have for this thread is about the A/c override wire from my Mishimoto fan controller. Where do I splice that into?

Do I splice it to the low-speed or high-speed wire on the rad temp switch?

[JonsE30]

i've read through this and of course i am also confused. it seems there are different applications for different e30's. i couldnt figure it out so i currently dont have the pigtail plugged into the temp switch on the side of the radiator, and my resistor broke so i have it bypassed and all 3 wires at the bottom my aux fan in my front bumper are connected to each other. fuse #3 has 30A blade in it. the aux fan turns on when i press the snowflake button.

i have a 1991 318i. i am looking at the switch on the passenger side of the radiator. the plug had 3 wires going to it 1 top, 1 left and 1 right. The connector was so brittle it cracked and exposed the wires as black, black/brown and black/green. i am assuming it is for ground, low speed and high speed but i do not know which wire is what and where on the plug it goes to. it doesn't seem to match up with the colors people are mentioning here. once i figure out the 3 wires and their orientation to the plug, i can slide them on to the right post in the plug, or buy a new pigtail connector and it should be all good according to factory.

i did see a post here that said: black/brown to green/black is high speed, black to green/black is low speed. These match the color wiring i have so does that make the green/black the ground?

i bought a new resistor, so when its mounted in, do i connect the 2 smaller wires on the right post and the 1 thicker wire on the left post? or does it even matter as long as two thin wires are together and separate from the thicker wire?

[radr]

For those with 82C temp switches, what temp does yours actually kick on?

I just pulled my 82C FAE/Facet switch and tested it, average temp it kicked on was 90C and turned off at 79C.

Also, blew my 30amp fuse, anyone use slow burn fuses? My father uses them a lot and suggested I use it for this application.


Also, do not bother ordering the Febi 82C from FCP Euro, it is labelled "90-95" and "01102" which would make it a 91C fan according to some cross posting, I told them and told them it should be marked "03280" and they shipped me another 91C switch. I tested both, kick on around 95C

So... I just ordered this same part from ECS in December (https://www.ecstuning.com/b-febi-par...72-slash-82~f/) – marked as 82 C. Engraving on it is 01102 which is a 91 C switch like this post suggests. I'm going to contact ECS tomorrow and try to find another source... FCPEuro (https://www.fcpeuro.com/products/bmw...-6131136427291) still lists it as an 82 C switch under E30 fitment.

Edit: FCPEuro has another switch listed (https://www.fcpeuro.com/products/bmw...h-61311364274c) which is both described as 82 C and the correct Febi part number (03280). I highly recommend searching via the Febi part number and ignoring whatever OEM part numbers exist.

[tenkaichibudokai]

I�m trying to use my stock aux temp switch wiring for my M10 engine (E30 chassis) but when I do the test to short the two wires the fan doesn�t come on. I checked on the fuse box and noticed that fuse 18 and fuse 3 are missing one of the spade connectors (as seen on the pics) what type of wiring do I need to do to make my stock temp switch connectors work? Thanks! Enviado desde mi iPhone utilizando Tapatalk

Update: I was able to make it work but now when the thermo switch reaches operating temperature (82 celcius) the fan starts working but doesn't stop unless I turn off the car.. any suggestions?? Enviado desde mi Nexus 6P mediante Tapatalk

[isaac.delgado]

I’m trying to use my stock aux temp switch wiring for my M10 engine (E30 chassis) but when I do the test to short the two wires the fan doesn’t come on. I checked on the fuse box and noticed that fuse 18 and fuse 3 are missing one of the spade connectors (as seen on the pics) what type of wiring do I need to do to make my stock temp switch connectors work? Thanks! Enviado desde mi iPhone utilizando Tapatalk

[Sladek]

read through many posts on here but unsure if my setup is working properly (from previous owner).

currently my pusher fan runs on low all the time and the temp switch (maybe a low temp one but unconfirmed) will trigger the high speed if it gets hot enough.

what I want to know is should the fan kick on high when the AC button is pressed? if not is there an easy way to make this happen? is there an AC relay in the fuse box that could jump the high speed relay?


Sent from my iPhone using Tapatalk

anyone?

[Sladek]

read through many posts on here but unsure if my setup is working properly (from previous owner).

currently my pusher fan runs on low all the time and the temp switch (maybe a low temp one but unconfirmed) will trigger the high speed if it gets hot enough.

what I want to know is should the fan kick on high when the AC button is pressed? if not is there an easy way to make this happen? is there an AC relay in the fuse box that could jump the high speed relay?


Sent from my iPhone using Tapatalk

[pandaboo911]

Official Electric Fan wiring thread!

Thanks for the help, it was indeed not enough voltage. I now have the 12v supply wired direct to the battery. The system works perfectly now, except this means the fan will obviously stay on even after the car is off. So I now have the same problem as “She loved E” below.



I have the same problem as this now. My car is quite modified and I don’t have the stock acc fuse box any more, where is the best place to find switched acc power for the fan?

If you have a manual sunroof or manual windows you can use the C302 Accessory connector under the dash.

In my car socket A has 12v in run which is normally for sunroof and socket Q has 12v in run which is for power windows. My car has neither power sunroof or windows so they are both unused. The stock aux fan draws a lot of amperage especially as it gets old, so this is not the best way to do it, but power windows are fused for 30 amps so the wiring *should* support it.

A better way would be to add your own aux fuse + relay box, get power from the main B+ lug inside the e30 fuse box with a ring terminal, and switch the relay using the fan switch. That way your fan can run even after the car shuts off. Many OEMs do it this way.
My VW vanagon for example, the fan runs 20-30 seconds after shutting the car off on hot days.


C302 diagram