When I purchased my 3d printer, I bought it from a previous owner who was in the middle of upgrading the hotend and the extruder configuration and had not thoroughly tested it. After looking at the fan configuration, I noticed that the extruder fan had not been on when the printer turned on. Instead, the part cooling fan was constantly on, which was odd since my smaller printer, the ender-3 has the extruder fan on all of the time and the par cooling fan only when needed during prints. This became an issue for the performance of my prints.
I asked about this in a 3D printing discord community I am in, and I got a response saying this was not normal for my printer and the wires must have been mixed up when hooking it up to the motherboard. This was an issue. The previous owner installed a power kill switch to the extruder motor and fans and had rerouted the power to it. If I wanted to swap the fan plugs, it wouldn’t be as easy as unplugging the cable and plugging it into the correct connector again. So I checked the voltages of the fans instead to see if it would be as easy as cutting and swapping the connectors from the extruder, and luckily yes, they were the same amount of voltage and amps. So I felt somewhat safe cutting and resoldering the connectors.
As that was my first experience ever soldering anything together, I was nervous. Still, luckily, after applying (admittedly too much solder) to the wires, I wrapped it in electrical tape, and it worked! After about half an hour, I had both fans working, including changing the speeds.
for reference photo of a blower fan (aka a part cooling fan):
