For hunting this issue, I would start with megaohms, and see if the resistance is stable, and then go smaller. If the number shown on display is not stable it is either out of range or you have oil on the rails or something which disturbs contact. Best would be to clamp one measuring tip to rail or foot with a clamp.
Note that like when Darren had this issue, as long as only one stepper wire has a short with rail or foot, the machine still might work without issues. It’s when you ground the machine that the issue shows up. Or when two or more stepper wires have a short through rail/foot. In the first case the motor error shows up when you ground the rail or foot, in the second case possibly always.
In both cases any short between stepper wire and rails is a fault.