John,

I've been working with this type of board quite a bit recently. Your original assumption would seem to be correct to me, that the centre GND pin on each of the connectors on your board should be connected to both common pins on the pair of switches you use for each axis. The X+ board connection should go to the NO connection on the limit switch at the positive limit of travel on the X-axis and the X- board connection should go to the NO connection at the negative limit of travel.

The ATmega328P microcontrollers used on these boards only use three input interrupt pins for the end stops - one for each axis, so you will probably find that the X+/X- header pins on your board are connected in parallel anyway. You should be able to confirm this by examining the tracks on the board or with a multimeter.

I have documented connecting end stop limit switches to a similar board to this on my website at https://capellacnc.co.uk/electronics...es/project.php and also show how I connected z-axis limit switches in parallel when only one controller board pin header was available in Step 14 on https://capellacnc.co.uk/electronics...er/project.php

Hope this helps!

Steve