Now it is working great with the mc.SignalSetState method per Daz assigning an unused input to the LED such as input63 as he suggested.
For those trying trying to use this, note the change to ISIG_INPUT from OSIG_OUTPUT ( 1=on 0=off) This code is in my PLC script.
As Daz suggested, I tried but do not have a ~ sign on my keyboard so stuck with >=.1 instead of ~= 0. It works better because there is noise below .1v
if tonumber(regval) >.1 then
mc.mcSignalSetState (mc.mcSignalGetHandle ( inst ,mc.ISIG_INPUT63 ), 1)
else
mc.mcSignalSetState (mc.mcSignalGetHandle ( inst,mc.ISIG_INPUT63 ), 0)
end
--
I could not get reliable function with the scr.SetProperty method. Sometimes it would work and sometimes it would switch to off and stay off.