Thanks for the answers, yes that cleared it up a bit. I have identified the GND and positive lead, I have already tested the fan with DC voltage, but at its rated 12V it obviously was running at full speed, I could get it to run slower when I lowered the voltage, tested down to 8V.
I have not a Dell motherboard, I bought this fan solely to build a 3D printed fume extractor.
Im just not sure about the PWM lead and the Tacho lead, since Dell does not follow standard fan wiring, and internet gives conflicting answers, thats why I asked about the risk if getting those two wires mixed up? I read that the PWM control signal is 5V I think?
I have seen that fan controller shown in the previous post, on Amazon, but I didn't see a potentiometer on it, to adjust the fan speed, but maybe thats done from the button?
I went ahead and bought a cheap PWM Speed controller to try it out, its called "Motor Governor ZK-MG" and supposedly has an adjustable frequency between 1Khz and 99Khz, and adjustable duty cycle between 0-100%. Bought it just to see if it works?
There is this writeup over at the overclockers website that shows how to build a dedicated PWM fan controller with very few components, its for a 5V PWM fan, but it says that the build for 12V fans is almost the same except that one should instead use a 556 and an extra resistor.
If somebody knows if that schematic on that website is correct and should work fine with a 12V, 3Amp fan I would be glad to get a confirmation that it looks okay?
My concern is that my fan can draw up to 3Amps.
Its this website:
https://www.overclockers.com/pwm-fan-controller/