battery cut off switch

i was told i need a battery cut off switch in my car to race at the track, because my batteries in trunk and faster than 11.99 , how do i hook it up? cant just be a cut off to battery that seems to easy and car would still stay running off of alt?

Moroso part number 74101 for use with cars running an alternator. Part number 74100 for cars w/out an alternator.

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