New guy here. I have an old miller thunderbolt given to me by a nice older gentleman. It worked a week ago in his shop. He brought it here to show a group of us some advanced stick welding tech. He is a master welder with 35 years of experience. We were bumbed that the welder would not work. Tinkering around it seemed that the switch was bad so I replaced it. Now when I try to turn it on I get a heavy arc in my sub pannel! I have double and triple checked that I hooked everything up right. I am bringing 70 amps over from the main so I should have enough juice to get the welder going. My guess is that there is a big short in the coil or something, Any advise would be greatly appreciated.Matt