OK, as you say it works.
the problem is that until you press ENABLE, the M8 function is active, so the pump works.
I would like Mach4 to start with the pump off.

there is no solution?
how can I assign M9 (to turn off the refrigerant) when I press ESTOP?

Put your E STop signal in the SigLib in the screen load script.

[mc.ISIG_EMERGENCY] = function (state)
    if (state == 1) then
       local Coolant = mc.mcSignalGetHandle(inst, mc.OSIG_COOLANTON)
       mc.mcSignalSetState(Coolant, 0)
    end
 end,

I'm sorry, I forgot to answer.
IT WORKS!!

daniba,

(Is it possible to add a sound to the "Change tool" LED?
A simple "beep" at every impulse would be excellent.)

Did you get the sound to work when tool change led is flashing?
If so how... with details please

Thanks

No sorry.
I didn't make any changes, I just left the LED.
I intended to parallelize a buzzer with the LED.
the two objects have different power supplies (led / buzzer) and I didn't know how to do it, so I left it unchanged.