Danno Hi, I have the same version. The 2 pads labeled 'KEY' are in parallel with the push button switch. I assume that's so you can connect your own remote switch (maybe foot-operated) to use instead of t... Hi, I have the same version. The 2 pads labeled 'KEY' are in parallel with the push button switch. I assume that's so you can connect your own remote switch (maybe foot-operated) to use instead of the push button if you want. They provided 2 pads for an LED but didn't install it and didn't provide one in the kit. Watch the video on u tube ( watch?v=PB0znkuYR7Y&feature=emb_logo ) and you can see what the LED is used for. Since there's a piezoelectric speaker included, you don't have to have the LED since either one will indicate what mode the welder is in. Note that they incorrectly printed a symbol for a quartz crystal in the location where the electrolytic capacitor goes. Also note that they marked the positive pad for the capacitor. The capacitor positive lead is the longer one. The negative lead is shorter and is marked by a dashed stripe along the side of the capacitor. Ver Más