Miller Spool Gun Wiring Diagram . Hello, i have a millermatic 200 s/n je744568, it's old enough that it has the 4 pin plug to connect the spool gun to it. Here is supposed to common. Miller 30a Spool Gun Wiring Diagram from wiringall.com Does anyone have the actual wiring diagram for a miller 30a spool gun. This wiring diagram is for rvs with factory 30a shore power and will show you what you need to install up to 1200w solar and a 3000w inverter to your existing electrical system. Diagram wiring welder lincoln gun spool miller arc mig spoolmate alternator resources wire.