Hello all. I've got a question for you. I see a lot of new car/truck fans, and they no longer use just a normal 12v hot/ negative ground. They all seem to have an extra white wire, sometimes green. I know this is for PMW control. Is there an easy way to use these new style fans in a retrofit application, and how do you wire it?
I have seen the Derale controller called "pwm", but it doesn't control a pwm fan according to the instructions. It just makes a variable speed fan, with only a two wire hookup.

Fans have no idea what's sending them the juice. All PWM does is chop teh supply voltage to the fan to control speed. basically it's on/off/on/off from the controller with longer ON times when it needs more speed. No reason any 12v PWM controller with sufficient current capacity couldn't be used to do this. Tons of cheap ones on amazon.

The fans I'm referring to have 3 wires; large gauge hot and ground, then a much smaller gauge 3rd wire. They will not run with normal positive and negative hooked up. This is the same for all new fans I can find . Apparently the small Dia wire needs a signal.....

if you look at the mercedes big fan thread, a member here made a controler for it.
there are 2 versions, 1 will run with just a hot and ground with a hot to the pwm wire.
the other version will eat itself shortly after you wire it up.
there were pictures so you can tell the difference.

I think you also need to know the frequency at which the fan operates. Maybe that can be done with a square wave generator (just a guess).

Here's a document with some good info on an aftermarket PWM controller that can control both OEM (GM) and Spal fans. There's also a diagram on page 13 that shows how to wire a single or dual fan setup.

Link: https://www.lingenfelter.com/product/L460320002.html Go to bottom of page and click on "View Instructions" button.

Hope this helps

I used the Mercedes fan with Howie's controller. Worked great. Is Howie still on here? Maybe his Mercedes controller would work with other fans, too.

Yep, I check in from time to time I recall someone wanting to try my controller with a BMW fan, but I never heard back if it worked or not.

As noted, there are two main styles of fans.

"Dumb" fans, with only power and ground wires, and no built in computer. Apply power and they turn on to full speed. Controllers for these need to interrupt the power to control the fan speed.

"Smart" fans, with power, ground, one or more control lines, and a built in computer. Input a PWM at the right frequency to the control line, and the built in computer will then control the fan to the commanded speed.