Hurco KM3P retrofit

What are the chances of one of the limit switches being faulty or miss wired? The switches should have 4 wires, 2 for normally open and 2 for normally closed, the normally closed ones should go to the drive.
If you wire RAC and FAC to the switches, do both wires give 15V at the drive?

Unfortunately the limit sw are fine, in fact I simply put a direct jumper on the +15 volt driver to FAC and RAC that is why I know that the servo driver is defective because the failure only occurs in the z-axis servo driver and not in the two other servos drivers making the same connection.

I suspect that there will be problems rigging up FAC and RAC to anything in HAL, as a servo system naturally dithers when stationary. Certainly don't try using an electromechanical relay.

PWM and DIR of Mesa analogue outputs are not obviously available, but can be found. If you start LinuxCNC from the command-line you will get a listing of the Mesa card pin allocations. You can then see which GPIO pin has been allocated to the DIR line, and use that. Something like hm2_5i24.0.gpio-0000-out

But, a better plan might be to use a "wcomp" on the output of the pid component, and then drive each of FAC and RAC with the under and over outputs with the min and max set slightly below and above zero to leave a small anti-dither window around zero.
linuxcnc.org/docs/stable/html/man/man9/wcomp.9.html