How to remove an after-market alarm

Updated July 20, 2017

At times, it is better to remove an old car alarm than attempt to repair it. For example, a key fob may become misplaced, lost or broken and the alarm won't work. Poorly supported aftermarket alarms make finding a replacement fob challenging. They're also problematic because ignition wires are cut during the installation process, often leading to no-start conditions when done improperly. Alarms can also go off for no apparent reason, yet another annoyance. Removing inferior alarm systems solves these problems.

Raise the bonnet of the car and disconnect the negative battery cable with a wrench.

Open the driver's side door and remove the panel that covers the bottom of the driver's-side dashboard with a screwdriver. Locate the alarm module; a black, rectangular box about the size of a human palm. A good way to be sure the box is the alarm is to locate a small, stiff wire that extends from one end. This is the antenna wire that picks up the signals from the key fob. Use wire cutters and snip any retainers, such as zip-ties, that hold it in place. Pull it out so the wiring harness is accessible.

Note the colour and size of the wires. The two large wires coming from the module that are the same colour splice into the ignition wire. Follow these two wires to the ignition wire coming out of the steering column, cut them out of the circuit, and use wire crimps to reconnect the ignition wire. Be certain this connection is secure. The car will not start if it is not a secure connection.

Disconnect the black wire that goes from the module to the body of the car. In some cases, this wire is spliced into the wiring harness. Either way, disconnecting this wire disables the alarm completely by removing the ground, or negative circuit. Reconnect any cut wires and wrap them in electrical tape.

Follow the same procedure with the remaining wires. Follow each wire and disconnect it where it splices into the power circuit, door lock circuit, headlights and horn. Snip the wire out of the circuit, repair the splice with a new wire crimp, and tape the repair with electrical tape.

Reconnect the battery and start the car. If there is a problem in starting, double check the ignition wire repair and make sure the repair is sound.


Some alarm installations include a separate alarm horn mounted under the bonnet. It is completely disabled when the module is removed. It is bolted in place and not difficult to remove. Follow the small wires that go from the module, through the dashboard, and into the engine bay. Locate the wire under the bonnet and trace it to the alarm horn.

Things You'll Need

  • Wrench set
  • Screwdriver set
  • Wire cutters
  • Wire crimps
  • Electrical tape
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About the Author

Jack Hathcoat has been a technical writer since 1974. His work includes instruction manuals, lesson plans, technical brochures and service bulletins for the U.S. military, aerospace industries and research companies. Hathcoat is an accredited technical instructor through Kent State University and certified in automotive service excellence.