In the case of press welders controls are usually located on the machine or nearby on a permanent stand or mount. Frequently they are mounted so they can be accessed by the operator standing in the front of the machine but sometimes they are mounted on the side of the main body of the machine.
A sketch of a normal mount on a machine is shown.
The control is shown on the side just above the transformer tap. The control could be adjusted by an auxiliary-plug in key pad or remotely by cable. Many controls have control panels build into the cabinets, like the panel shown here.
Reference: RWMA - Resistance Welding Manual 4th Edition