My 1970 Miller big 40 will start up and run but won't weld now. Just got done doing some work to the motor but didn't really touch the generator side of it except that I put a new range selector switch in it. Not sure what's wrong was welding before got the switch with the welder old 1 was really lose so put the new 1 in. Not sure what I could have done to cause it not to weld any help would be appreciated thanks