Official Electric Fan wiring thread!

[grinchxvx]

For those who have their cars on the 80/88c what would cause the high speed to not kick in? I have it wired pretty similarly but j use the snowflake button just because in the winter it gets so cold that I may not need the fan on at all but I can't tell if it's kicking onto high mode or not.


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[MattPro]

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.

I know this post has good intentions, but there is definitely some misinformation in here.

For starters, the DME will not "cut fuel" because the coolant is too hot when starting. The temp switch on the radiator is only used to control the high/low speed relays, not fed back to the DME. The DME reads the temp from the temp sender in the thermostat housing. If you are having hesitation during hot starts this sensor is probably bad, and the DME is reading that the engine is colder than it actually is so it is enriching the mixture to compensate for a cold start causing hesitation.

Secondly, when the engine starts cranking and the alternator starts putting out 14v this shouldn't cause you to blow a fuse. It is probably because you were trying to start the fan on high speed on the low speed circuit. When the fan first starts its current draw will spike, and if too low of a fuse is used it will blow. Maybe when your fan automatically turned on when driving it was already spinning so it didn't draw as much current, but the change to 14v definitely would not blow a fuse, otherwise everytime your fan kicked in while the car was running at 14v the fuse would blow.

[Heitzke]

Just finished mine up, thread was very helpful. Spal 16" pusher on a M42 radiator.

I ended up wiring mine differently, but with the same components as everyone else. Forgive my picture of a screen (lol) but this is what I did:



I didn't end up tapping power for the rocker switch, so I just don't have a light on it. Generally, using the rocker switch and/or the temp switch to act as the ground for the circuit.

[JamesE30]

Fan wont work unless I tap the relay... ??

Hey guys, need some help with a strange problem,
I have wired up my new 16" SPAL Pusher exactly as described by Klug.
I have all new wiring (12GA), a new 82* single speed fan switch, and new relay as pictured below.

With the thermo switch activated (or bypassed) The fan will only turn on if i physically TAP the relay.. with my finger..
Just a light tap does it, but if i don't touch it nothing will happen.
Here is a quick vid showing what I mean.

https://www.youtube.com/watch?v=oTann85ZvhI&feature=youtu.be

I have tried this with 2 brand new relays and they do the exact same thing. The whole system/switch/fan works perfectly, but the fan wont turn on until i tap the relay.. I'm baffled?? Any ideas?

This thread has been super helpful so far so thanks to everyone who contributed!

[Mark 42]

Wire diagram confused me.

I want to move the aux fan (low & high speed) to a circuit that is on whenever the ignition is on (sometimes my temp gauge climbs a bit high when I sit at a stop w/o A/C on).

I only recently found out that the fan is only available when the A/C is on, but even knowing that, I would rather have the circuit live when ignition is on, and controlled by the temp switch.

Looking at the wiring diagram, I saw a 30A fuse (#20) and a 7.5A fuse (#19) in the same circuit (?).

I'm trying to figure out where I should disconnect the supply which comes from the snowflake switch and splice in an IGN controlled power source (or control voltage, if the source for fan power comes from a relay, and the snowflake circuit just activates the system).

[Razor1981]

Great write up

One of the things I need to take care of yet. Gotta make it. Great write up. Really should be a sticky

[vaughnbannister]

Good write up!

[328ijunkie]

need to try to bleed better. The ETA radiators can get airpockets trapped up by the sensors and then they dont work. Thats why they lowered the port down on later radiators.

[DirtyThurdy]

Hey all,

I recently purchased a 84' 325ES that had an electric fan and no clutch fan but the electric fan was wired always hot so the motor never got to the proper temperature.

I purchased the relay, wiring and switch listed in the OPs original post. The problem I am having is the switch never closes when the engine is up to temperature.


I installed the new sensor in the lower port on my radiator, it gets warm but not so hot you cannot touch. I do not think I have an air bubble in the system as the heat blows hot.

I am wondering if the sensor I bought is not the right one for my setup? maybe I need a lower temp one for the location on my rad? I have confirmed my wiring is correct by shorting across the temp switch and the fan comes on. Also when removing the top sensor no fluid came out of the rad but fluid did come out of the lower port when installing the new switch....



Thanks for any help!

[NeverEnough02]

Low speed is sufficient in most applications, it just runs a little longer, which isnt necessarily a bad thing either. Some applications/climates require high speed to wash off all the heat. M42 radiator + Florida for instance

Got ya. I am in new england but would like to be prepped for the worst since we have heavy traffic at random times. I have a brand new 325 radiator.

[328ijunkie]

Low speed is sufficient in most applications, it just runs a little longer, which isnt necessarily a bad thing either. Some applications/climates require high speed to wash off all the heat. M42 radiator + Florida for instance

[NeverEnough02]

I have an M50nv.

After reading through this, I am stuck between ordering the 3 pin 80/88 to retain the 2 speed OEM fan functionality vs. ordering the 82* 2 pin for the fan to kick on high right away.

I am thinking if the fan is already spinning at the slow speed, when it kicks up to high speed, there will be less strain resulting in less blown fuses like others have experienced. Does the low speed really not push enough air through the radiator to start cooling?

Also, 61311364272 is a 92* switch part number according to bav auto. This means that high speed will kick in after it would with the 80/88 switch.

Help me decide!

[NeverEnough02]

Why is this not a sticky yet?

[328ijunkie]

Very weird if snowflake fires aux fan. Usually diode being fried prevents fan from firing when snowflake is pressed...

and thanks klug, added to first post!

[GDA]

Question - I have a 16 inch pusher fan wired in on the factory aux fan wiring harness. Just this past weekend the low speed circuit quit working and jumping the terminal would not engage low speed. High speed circuit works. Relays swapped with no change. All fuses good and swapped with others to double test with no change. Checked continuity on black wire to fuse box and low speed wire has continuity.

Aux fan does engage when you press the snowflake button... Does this mean the diode in the fuse box is bad?

A bit stumped by this one as temp switch is good and resistor is good as well. Even swapped in a new resistor with same results.