Some Dupont wires solder poorly.
Wires are antennas, both transmitting and receiving.
Since I have it, DMX cable works for PWM signals. USB cable would be another option.
Consider short power leads from 12VDC supply to motors instead of overkill gauge.
Stranded copper insulated 16 AWG twisted pair wires looped thru a ferrite bead
would be my preference for power:
FWIW, I use STM32 and ESP32 boards with Arduino code,
instead of Arduino microcontrollers.
STM32 and ESP32 support more PWM pins without bit banging,
allowing a single controller to drive both fans and harness tensioners
as well as e.g. input switches.