All you need to know about Battery Cutoff Switches

What is a Master Battery Cutoff Switch?

Let's start from the beginning. A Master Battery Cutoff Switch is an important safety feature in motorsport. It helps prevent alternator circuit damage due to voltage surges but more importantly, it stops the engine automatically when turned off, preventing "run-on". It also serves as a simple and effective anti-theft device for competition vehicles.

If you are involved in motorsport in New Zealand you will need one as per Motorsport New Zealand Schedule A. Which has the following rule:

Ignition Switch / Circuit Breaker (Kill Switch): All vehicles shall be fitted with a spark-proof ignition switch/circuit breaker as follows:

• It shall be capable of breaking all circuits that keep the engine running, including the ignition, fuel pump and alternator, and
• Series Production vehicles may retain the use of the original ignition switch where it meets all of the above requirements in (a), and
• Where the Series Production ignition switch is not used, one shall be positioned within reach of the occupant(s) (both) while in their normally seated position with harnesses worn.
• The ignition switch/circuit breaker shall be clearly identified (refer Diagram 5.4(1) below) except where the Series Production ignition switch is retained.
• For Closed Dedicated Motorsport Vehicles competing in Race Events, an external ignition switch/circuit breaker shall be fitted, located near the bottom of the windscreen. It shall be marked by a red spark in a white edged blue triangle with a base of at least 120mm (refer Diagram 5.4(1) below).

The most common cutoff switch we sell is the Grayston Master Battery Cutoff Switch available here.

Here’s one installed under the bonnet right next to the battery. This keeps the heavy battery cables as short as possible. However, depending on your vehicle you might have it located on the dash or within reach of the driver.

It’s relatively easy to install with some basic tools and wiring knowledge.

Here are the wiring instructions and a couple of things to note. You need to cut the power to the electrical system and shut off the fuel pump. We've seen some that didn't and that's not only dangerous in an accident but they won't pass inspection. When wiring it up make sure you connect the right wires to cut everything. 

If you’re mounting this under the bonnet or in the cockpit you’ll need a pull cable. The Grayston Pull Cable is 1.5m long. This means you’ve got plenty of cable to mount it where it will be visible and easy to pull in an emergency situation.

Last but not least you’ll need a sticker kit to make sure you’ve clearly marked where the cable pull is. The Grayston Scrutineer Sticker Sheet has all the stickers you need to be within the rules and be safe when you’re racing. Here's an example by the windscreen.

Protect yourself and your car in case of an accident with a simple Master Switch cutoff. They make it easy to know when the power is off when you're working on your car too. Buy one here.