http://www.millerwelds.com/service/ownersmanuals.phpOwners manual is here, it has the electrical diagrams for the machine, you need your serial number to insure the exact correct one.
It appears that there are two switches that need to be set to remote. One is the contactor control, the other is the amperage control. The contactor itself seems to be mounted in the lower, front, left part of the machine as you face the front panel.
Bill