I/S CONTROL SWITCH REPAIR
Replacements for the START/STOP and SINGLE STITCH switches can be found at Radio Shack. Catalog Number 275-609A contains one red and one black switch.
Pull back the foam handle and carefully pull off the rubber sleeve and the switch from the handle.
Inspect the wires and the splices for broken contacts or short circuit. If no visible problem is found, the malfunction may be caused by a part inside the switch.
While holding the switch upside down, as pictured below, unscrew the endcap from the switch.
Remove the springs and contacts from the switch and inspect them. If any of the components are bent or broken, replace them with parts taken out of the new switches.
When putting the switch back together make sure that the large spring sits firmly inside the body of the switch and the small spring goes into the recessed part of the endcap (shown by the arrow).