Abstract: A method of indirect spot welding two or more members together, comprising the steps of pressing electrodes against at least one of the members, flowing a square wave current between the electrodes and across the members during a first time period, pausing the flow of current, flowing a square wave current between the electrodes and across the members during a second time period, and stopping the flow of current.

Abstract: A spot welder comprising a movable truck which is movable along a workpiece, and first, second and third electrodes supported on the truck. The first and second electrodes are adapted to pair with each other for series welding, and one of the first and second electrodes is adapted to pair with the third electrode for indirect welding. Depending on the state of the site of the weld, welding can be performed by selectively using either series or indirect-spot welding. Mechanisms are provided for easily and rapidly switching between the two welding types.