Yes, I know this is an Old thread, but I wanted to give an update on using the Vulcan 160 spoolgun on a Miller 140 which has the small 4 pin plug. It was made to use a Miller spoolgun with it. The Miller 140 was wired to have a switch installed so that you could change between the onboard wire feeder and the feed motor that is in the spoolgun. The 4 pin plug has all 4 pins populated so that 2 of them are for the trigger and the other 2 are power to run the wire feed in the spoolgun. What I found was that the power for the spoolgun needed to be reversed because the Vulcan 160 would pull the wire back to the spool instead of pushing it out of the gun. Once the polarity of the red and blue wire in the Vulcan spool gun was swapped it now works like it was designed to with the Miller 140. I hope this helps someone else trying to use the Harbor Freight spoolguns.