Might be a safety issue and I suspect the blue wire is a sensor out to the control circuit called Tach.

Blue wire with eyelet was definitely captured by a screw and serves as a grounding to the vehicle chassis.

 

When you say a low side switch you mean using a PWM that will turn the negative on/off?

Correct.

And fortunately, low side PWM modules are quite common, in fact you would be hard pressed to find a high side one. (They are available but as rare as the dodo)

There also some with variable frequency as well as duty cycle...something you might want to consider.

 

The fact that putting 12V on the wire had no effect, but grounding it does, means that the input is likely pulled up internally. That is why I asked you to measure the voltage on it. That voltage would tell you what a safe PWM voltage would be.

But simply using a low side switch to ground to ground it would always be safe. So go ahead and try the circuit posted by @sghioto.

 

The fact that putting 12V on the wire had no effect, but grounding it does, means that the input is likely pulled up internally. That is why I asked you to measure the voltage on it. That voltage would tell you what a safe PWM voltage would be.

But simply using a low side switch to ground to ground it would always be safe. So go ahead and try the circuit posted by @sghioto.

So hook up:

Black to ground
Red to +12v

Then measure white wire voltage using volt meter leads from White to Ground?

 

I found this module on Amazon I think will work if you don't want to assemble my circuit.
Just need to add a diode in series with the PWM white wire.
NE555 Duty Cycle Frequency Adjustable Square Wave Signal Generator Board Module by Envistia Mall

 

@sghioto Thank you.

What about this one Amazon ? This one has prime delivery tomorrow. If this one would work, is a diode needed as well? Any particular type of diode I would want to use.

 

Looks like the same. Yes would still need a diode.
The diode is there to block the DC voltage output from the module when the output is high which is appx 11 volts.
Thus the PWM only sees a low signal
1N4001 diode should be safe enough.

 

@BobTPH

I measured voltage from PWM wire to ground and it was 4.751v

 

I measured voltage from PWM wire to ground and it was 4.751v

Then the module with the diode should be fine.

 

Then the module with the diode should be fine.

Do I want to limit the input voltage to the module to 5v or is a full 12v ok?

 

12 volt is OK because of the added diode.
Remember this is experimental but I believe the module will work.

 

12 volt is OK because of the added diode.
Remember this is experimental but I believe the module will work.

Is it strange that the fan doesn't work with 12v applied to the PWM wire? Or is it simply one of those things where the fan wants to see the modulated signal.

Should I try 5v to see if that will run it on high speed?

 

Or is it simply one of those things where the fan wants to see the modulated signal.

Correct.

Should I try 5v to see if that will run it on high speed?

I suppose so since applying 12 volts didn't damage anything.

 

@sghioto @BobTPH

I hooked Red and Black to + - respectively and then applied 5v to the PWM wire and the fan does nothing. Does that change anything in your analysis? Do we still think the square wave generator might be the answer?

 

Does that change anything in your analysis? Do we still think the square wave generator might be the answer?

I didn't expect that to work but it was worth the try. The module should work with the added diode.

 

@sghioto

Will this DIODE work?

Probably bigger than we need, but I happen to have a few of these in my electrical junk drawer.

 

That will work!

 

@sghioto @BobTPH

I tried the module from Amazon with no success. I put the diode in between the module and the PWM wire.

With DVM the output wire from the module was around 3.8v Should I have seen it going from 0v to 3.8v rapidly? When I saw no reaction of the fan I adjusted the two screws on the module.

I also tried again with the PWM wire to ground (module removed from the equation). Scratching the PWM wire on a ground causes the fan to operate. It's really weird. HERE is another video.

Any other suggestions?

Anyone have some spare time? I can send you the fan to see if it is something simple to figure out?

 

Any other suggestions?

Try adjusting the duty cycle of the module to read 2.5 volts on the DVM, then connect directly to PWM wire and see.
2.5 volts would indicate a duty cycle of 50%. The lower the DVM reads indicates a higher duty cycle on the low side which is what I think the fan needs.
Looking at the video the fan seems erractic at startup.

 

Try adjusting the duty cycle of the module to read 2.5 volts on the DVM, then connect directly to PWM wire and see.
Looking at the video the fan seems erractic at startup.

The video is me grounding the PWM wire and not using the module.