Abstract: In a capacitor-discharge breakerless ignition system for an internal combustion engine, a safety interlock comprising a rectifier and a switch responsive to a preselected unsafe vehicle condition is connected in the charge circuit of the ignition capacitor. The rectifier is poled in the forward capacitor charge-voltage direction and is connected with respect to the switch such that the capacitor is not charged or, once charged, is discharged prior to engine ignition in response to an unsafe condition indicated by the switch, or in response to intentional or accidental breakage and/or short-circuiting of interlock/ignition interconnection leads. The rectifier and the switch are packaged in such a manner, preferably separate from the rest of the ignition, to deter tampering with the switch alone, and to permit locating the switch and rectifier remote from the ignition circuit. In one preferred application the rectifier-switch package is mounted on the handle of a rotary lawn mower to serve as a deadman switch.