Abstract: An apparatus is disclosed for interrupting operation of a starter of an alternatively-fueled motor vehicle. The apparatus comprises a fuel receptacle, a cover and a switch. The fuel receptacle has an electrically conductive, grounded fill opening. The cover mates with the fill opening of the fuel receptacle, and has a contact sensor which generates a ground signal indicative of contact between the cover and the fill opening. The switch communicates with the contact sensor and with the starter, and interrupts operation of the starter when no signal indicative of contact is received from the contact sensor.