JazzCNC - I'm not ready to cut any wires yet, so please bear with me.

Doddy - using the multi-meter, when the switch is in the not-pressed state the white to red reading is zero and the white to black is 4.75v. With the switch connected and in the alarm position (led on) both readings are 2.25v.

HOWEVER (!) triggering the switch is no longer causing the status in gbrlControl to go to Alarm, although the console is still showing ALARM: Hard limit etc and I have to go through the reset process.

A quick question. Once the alarm has been triggered the only way I can get the stepper motor to turn and release the switch is to set $21=0, jog the motor, press unlock and then reset $21=1. Is that what I should be doing?

I do have a soldering iron etc, but I have also installed a connector block on the chassis, if I have to start rewiring connections.