Here is one made for Battery and Magneto, which would be different from one that shuts down an alternator.
Magneto & Battery Saftey Kill Switch
From Flaming River Industries
Dual circuit switch simultaneously shuts down both the battery and magneto. Waterproof spring-loaded design with silver plated brass contacts. Rated at 250 amps continuous service, 2,500 amps for 5 second surges. Accepted for NHRA/IHRA competition use. Furnished with an easy-grip T-handle, and anodized aluminum mounting bracket.