Solved Print bed fan won't turn on

When I first got my printer I was using ABS, so I unplugged the power to the fan that blows on the print bed. For whatever reason even when I turned the fan off in the MatterControl settings it would still come on, so unplugging the power fixed that problem. Now, I'm switching to PLA and having that fan on would be very helpful, but I plugged in the power for it, made sure the MatterControl settings are set to on, and the fan won't turn on. It does spin, and the power connector is plugged in all the way until it snaps.

Does anyone have any suggestions on other things I can check? If necessary I can check firmware settings, but my brief look at the configuration.h and other files in the sketchbook I didn't see a "fan on/off" control I could check.

Is there a guide to the hardware underneath the printer that shows which one is the power for that fan? Maybe mind is loose or plugged in backwards or something.

I decided to switch to PLA because I got tired of the ABS shrinking and lifting. So far it's printing very nicely, but I'm worried larger/taller prints will warp without the proper cooling.

 

Measure the voltage coming in

 

Just an update - I checked everything for the fan to make sure the fan itself wasn't burned out (it wasn't) or that the power cables to the fan weren't severed (they were fine). Checked the voltage on the motherboard for that fan and sure enough, the board wasn't feeding power to the fan. We looked through the config files and found that in the firmware version I had there had been some change to the fan pins, I didn't understand exactly what, but we downloaded and installed the latest firmware available and then the fan turned on just fine. The latest version also had some fixes I had to figure out myself last time, like the max bed temp being too low before and some z-axis adjustments so that was good. Prints beautifully now.