Yep just a motor wire to fallout while Jogging would fry lots of cheaper drives.!

Are you using the USB SS or ESS.? in either case they don't use Kernal speed but it's best to set it at default 25Khz.

If using ESS then look in Plug in control and choose ESS Config. On left you'll see Max Step Frequency for each axis and Spindle. Set to 128Khz you won't need any higher than that.