Drive motor on Mastercraft MIG welder stopped working.

Steve
Here is a wiring diagram for the machine. It doesn't do alot of good but is a bit of help
Main Circuit Chart - Mastercraft MIG Instruction Manual [Page 34]
If you are getting the click of the relay on the board then the gun trigger is good and the board is getting the 24v it needs to operate. Since you ran power to the motor and it spins then that only leaves what tooljunkie pointed to, the control board.