Fantastic. I love happy endings!
Check your vfd settings
Did reverse work before the coolant mods?
1. P16-Port1 LED should come on at either M3 or M4 - good to go.
2. Check Mach3 LED status on P14-Port1 when you call M3 and M4. Change state? If not, skip to #4 below
3. Check 126 board LED status on pin 14 same test. Or, if running PMDX-107 spindle board, check the 107 board DS-4 LED. See page 14 of 107 manual.
4. Double-check 126 board relay settings. For your setup JP2 should be "multi-mode" and Dip 8 - "Closed" (controls K2 with P14-Port2)