If you own a Shapeoko 3 that was released/sold pre-2019 when they updated their circuit board and in order to access the PWM signal you'll have a few extra steps to follow.

 

Not to worry.. you can still get the spindle working in automatic-mode… but it is harder to get going.

 

The PWM is also available on the 6-pin ICSP header on left side of the board,

 

The ISP header (on v2.4d and probably all boards going back to the dark ages) has this pinout:

 

pin 1 = D12 = MISO = LIMIT Z
pin 2 = 5V
pin 3 = D13 = SCK = SPINDLE DIR
pin 4 = D11 = MOSI = SPINDLE PWM
pin 5 = RESET
pin 6 = GND

 

What you’re after is Pins 4 & 6 which happen to be right next to each other.

 

The pins are arranged like this when looking at the board with the USB/power connector on the left side:

 

2 | 4 | 6
1 | 3 | 5

 

Thus those top-row middle and right side pin is what you need to connect into.

 

Something like this is what you’re after: https://www.amazon.com/ZSDZFYLLK-Pieces-Single-Female-Connector/dp/B0DN6TBYF9/

 

Plug the red wire into pin 4 and black wire into pin 6.

 

Then cut off the control cable and connect

black to black

red to red

 

From here you’ve successfully accessed the PWM signal and connected it into your vfd.