E. Stop signal error

Hi Group,
I'm getting fake emergency stop signals from my router / plasma
cutter. I have 3 Gecko 320s with their err/res wires joined together
connected to the "optional external fault LED circuit",( as shown on
the G320 PDF Manual ) and to the PC via a CNC4PC C10 breakout board.
I noticed when connected in this way the Geckos' fault light has a
constant dull glow, possibly due to pulldown resistors on the breakout
board.
I any case it doesn't seem to take much to E Stop Mach 3, sometimes
without tripping the drives.
This usually happens when the plasma starts or the router motor is
switched off. The Gecko's power supply ground is common with the
breakout board ground.
Thanks,
Glen.