Official Electric Fan wiring thread!

[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.

[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.

[carguy101]

Saving this for later. Thanks!

[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!