A small thing that may assist you is not to use motor outputs for testing the pins but the Mach Output #4, which is the default for coolant. Go into config, ports & pins, spindle set-up and remove the tick from 'disable relays'.
Use the output signals tab to assign Output #4 to each pin in turn. It doesn't matter if you set active low or active high. Then use the MDI to repeatedly do M7 M9 and you should see the pin toggle from 5v to 0v.