Wiring a new kit car, or rewiring an old one, can be frustrating, especially when you discover little problems at the end of the installation. When building a kit car, we learned early on the benefits of installing a cutoff switch in the system. Along with added security, the switch acts as a safety device to disable the electrical system, once the car is finished and on the road. It is easier to turn a key than to disconnect the battery cables each time work needs to be done on the electrical system.
We use a Cal Term Pro Battery Cutoff Kill Switch, designed for race cars. Its ruggedness also makes it ideal for street car applications. In a race car, it's mounted on the outside of the car, or up high on the dash in open cars. This switch also will prevent the alternator circuit from being damaged by high-voltage surges.
For our Speedster replica applications, we mount the switch under the passenger seat to keep it out of view, and rely on it primarily as a security device. The switch allows you to turn off the power when you are away from the car, and keep the key with you to foil would-be thieves.
About the only concerns you may have with this installation are devices--radio, clock, thermostat-controlled fans, or alarm--that require a continual power supply. Such gear can be wired directly to the battery through a separate circuit.
An added benefit we've found is that by wiring the switch to the ignition and coil, it prevents run-on by disconnecting the alternator circuit from the ignition circuit.
Regardless of the specific reason for an electrical cutoff switch in your project car, $15 for the device is an inexpensive price to pay for security and peace of mind.
