every plug is different
try this :
get a new plug new make sure you pull the coil out enough
now let the plug hanging on the cable and ground it.
set the voltage to 2.1 and look at the colour as you do a start , if its yellow-bright you are ok.
if its red it is to low , to high and you guessed it use a new plug.
this is the way if i use a different plug as jetcat supplies them.