Are you having issues with your spindle dropping RPM's and/or not fully stopping when told to go 0 rpms?  Then you likely have a loose PWM cable thanks to the Molex internal design.

The problem is these two pins are backing off resulting in poor contact between the PWM wires and the internal controller.

A simple solution here is to pull the wire out, press in these pins to fully seat them, then add some hot-glue behind the pins like this:  

Carbide Motion v6 observance: 

We have also seen in more recent models that require the warthog pigtail connector where during the Carbide Motion setup, they had previously selected bit runner forcing it to stay selected but ghosted and therefore de-selectable when choosing a spindle or VFD. 

Doing this resulted in any RPM commanded over 1000 would bring the spindle up to 24000 rpm. 

Theres a few reasons why this happened. 

First there is no code that travels over the wire between the controller and the VFD and the VFD doesn't accept G-Code. Its done with a voltage. Most controllers use 0-10v but Shapeoko uses 0-5v. 

This voltage is translated to hertz, and that hertz is translated to RPM's as its observed. This is another reason why when you command 18k rpm, it registers in a constant window between +/- ~2% (margin of error)

With a 2.5v on a carbide controller, that would equate to 200 hertz (on a 400hz motor), which would translate to roughly 12k rpm but since the Bit Runner was selected, once an rpm over 1,000 was commanded, it went full throttle. 

The reason why this happened was because the bit runner uses the same code to turn on and off, and has an open / closed status instead a variable status. Since the Bit Runner was selected, and its an on/off selection, the voltage went full when it was commanded an RPM greater than 1,000 registered since again the Bit Runner. 

For this and a few other reasons, this is why Bit Runner CANNOT be used with spindles.