Direct from the rule book.
8:4 MASTER CUTOFF
Mandatory when battery is relocated, or as outlined in Class
Requirements. An electrical power cutoff switch (one only) must
be installed on the rearmost part of each vehicle and be easily
accessible from outside the car body. This cutoff switch must be
connected to the positive side of the electrical system and must
stop all electrical functions including magneto ignition. The off
position must be clearly indicated with the word OFF. If switch is
push/pull type, push must be the action for shutting off the
electrical system, pull to turn it on. Any rods or cables used to
activate the switch must be minimum 1/8-inch diameter. Plastic or
keyed switches prohibited. Switches and/or controls must be
located behind rear wheels on rear-engine dragsters.