First, I have to tell you the Board Maker told me this in an email a couple days ago. Pretty sure this will influence the following tests. * The enable pin is connected to D13 and R1 is its pull-up resistor connected to 5v. I know these boards will move the steppers with the default GRBL settings so I would suggest reflashing GRBL to get a clean instance then trying again with the fixed board. When I’m testing, usually all I do is set $1=255 and $21=1. Once it moves, then configure the settings to match your machine. * That's what the Board Maker told me. Tried that a couple days ago. When testing Resistance between Enable pins, the resistor and D13 pin. I get what I would expect, Little to no resistance between enable pins, 10k ohm resistance resistor 10k ohm resistance between enable pins and D13. This goes for All enable pins, they are definitely connected. Nothing out of the ordinary. So what this tells me is the resistor is what is making the enable pin high. but what I don't understand, why won't Arduino set that pin low. I've tested D13 again to make sure that I didn't do something wrong last time. No matter what I do I can't get GRBL to set D13 Low. I've sent G Code, Jogged the controls in all directions, nothing. Still 0.5V. Isn't Arduino High supposed to be 5V and Low 0V? Why am I getting 0.5V? So I tried that code you wrote for enabling pin 13 high and then low. Worked Flawlessly. So my interpretation from this is GRBL is not doing it's job with D13.