How to Wire a Battery Disconnect Switch

  • 2-3 hours
  • Beginner
  • 35-60
What You'll Need
Ratchet and Socket Set
Battery Cable
Wire Cutter
Wire Strippers
Wire terminals
Terminal Crimper
Disconnect Switch

Installing a battery disconnect switch in a car can save lives if used in the proper situation. These switches are wired to a car’s battery and can be used to instantly cut the power to an engine in an emergency situation. So, not surprisingly, these switches are most often used in race cars where the odds of the driver being in a catastrophic crash are much greater than that of most drivers. Yet, there are some other applications, perhaps most notably anti-theft situations, in which a battery disconnect switch may be useful in a regular car. To learn how to install one, simply follow the steps outlined below.

Step 1 – Disconnect the Negative Terminal

Using a wrench, remove the connection on the negative terminal of the battery.

Step 2 – Drill a Hole

Drill a hole through the car to the area where the switch is to be mounted. Depending on what the switch is being used for (as a safety device in a race car, as an anti-theft device, etc.) different mounting positions may be desired. One good area to mount the switch is the dashboard where it can be reached easily by the driver in an emergency situation. To mount the switch here, pull back the carpet on the driver’s side and drill a hole into the engine compartment; be careful not to hit anything on the opposite side. Then run the wire up into the dash board. You will probably have to drill an additional hole in the dash to fit the switch through.

Step 3 – Cut Some Battery Cable

Using a wire cutter, cut a length of battery cable long enough to run from the battery, through the car and up to where the switch will be positioned. Once the wire is at the desired length, use a wire stripper to take off about 1 inch of the insulation on both ends. Then, using a terminal crimper, secure a terminal end to each stripped end of the wire.

Step 4 – Mount the Switch

Fasten one of the terminal ends now connected to the wire to the disconnect switch and feed the opposite end through the holes that were drilled into the engine compartment. It shouldn’t matter which terminal the wire is connected to on the back of the switch since it is only a simple on/off switch. Connect second wire to switch in similar manner. Once the wires are connected to the switch, mount the switch to the dash using the mounting nut that should have been supplied with the switch itself.

Step 5 – Connect the Switch to the Battery

Bolt the end of the wire opposite the switch to the negative post of the battery and re-secure the negative terminal with the socket and ratchet. Connect second wire to the negative battery cable. Remember to test the switch to ensure that it will work if there is an emergency situation.