Fan control circuitry, red plug is for the fan. Lose plug on the right connects the fan to the PWM HAT. Fan sits directly over the CPU.

Top fan board version 1Bottom of Fan board, version 1

Version #2 of the fan board. All for that slot for the DSI ribbon cable.

Top Fan Board version #2Bottom fan board version #2

Fan board mounded on Raspberry Pi

Fan board pluged into  PWM HAT

Version #2 mounted in the stack.

Fan version 2 mounted on Raspberry PiFan plugged into PWM/Servo HAT

Fan control push button

Fan push button was to be mounted out of sight under the track.

Switch moved to the Traffic Monitor bracket.