The modular pin spotting system described herein allows a common welding source to be utilized with both hand held pinspotters and fixed pinspotters. This allows the operator to choose the mode of operation for the welding source based on operator needs. In some aspects, the pin spotting system includes a mobile welding source, a ground handpiece, a handheld pinspotter apparatus, and a fixed pinspotter apparatus. The welding source is removably attachable to either of the hand held pinspotter apparatus and fixed pinspotter apparatus and configured to supply welding energy to the attached pinspotter apparatus. Each of the hand held and fixed pinspotter apparatus are configured to energize the mobile welding source to supply welding energy to a weld pin positioned against a sheet metal surface to affix the weld pin to the sheet metal surface through welding.