How To Make Cigarette Lighter Turn Off With Car

One of the minor annoyances in older cars, and even some newer ones, is the cigarette lighter socket (often repurposed as a 12V auxiliary power outlet) staying powered on even when the ignition is off. This can lead to battery drain, especially if you leave devices plugged in overnight. The good news is, with a bit of understanding of your car's electrical system and some basic tools, you can modify the circuit so the outlet turns off with the car. This article will guide you through the process.

Understanding the Car's Electrical System and Accessory Circuits

Before diving into the modification, it's crucial to understand the basics of your car's electrical system. Your car operates on a 12V DC (Direct Current) system. The battery provides the initial power to start the engine and runs the electrical components when the engine isn't running. The alternator, driven by the engine, recharges the battery and supplies power to the electrical system when the engine is on.

The electrical system is protected by fuses. These are safety devices designed to break the circuit if there's an overload, preventing damage to the wiring and components. Different circuits are protected by different fuses, and they're usually located in a fuse box, typically found under the dashboard, in the engine compartment, or sometimes in the trunk.

Accessory circuits are those that power non-essential components, such as the radio, cigarette lighter/power outlet, and sometimes certain lights. Some accessory circuits are designed to be always on (powered directly from the battery), while others are switched, meaning they only receive power when the ignition is turned on. The cigarette lighter is often, unfortunately, on a circuit that's always hot, leading to the problem we're addressing.

Identifying Switched and Unswitched Circuits

A switched circuit is controlled by the ignition switch. When the ignition is in the "on" or "accessory" position, the circuit is powered. When the ignition is off, the circuit is de-energized. An unswitched circuit, on the other hand, is always powered, regardless of the ignition switch position. Identifying which is which is crucial for our modification. We'll use a multimeter to determine this.

Technical Breakdown: How to Make the Cigarette Lighter Turn Off With the Car

The most common method to make your cigarette lighter turn off with the car involves rerouting the power supply to the outlet from an unswitched to a switched circuit. Here's a step-by-step guide:

Preparation and Safety:
- Disconnect the negative terminal of the battery. This is the most important safety precaution. Use a wrench to loosen the nut on the negative terminal (usually marked with a "-" sign) and carefully remove the cable. This prevents any accidental short circuits while you're working.
- Gather your tools: a multimeter, wire stripper/crimper, wire connectors (butt connectors or solder and heat shrink tubing), electrical tape, a fuse tap (add-a-circuit), and appropriate wiring (16 or 14 gauge automotive wire).
Locate the Cigarette Lighter Fuse:
- Consult your car's owner's manual or a wiring diagram to find the fuse for the cigarette lighter/power outlet. The manual will show the location of the fuse box and a diagram indicating the function of each fuse.
Identify a Switched Fuse:
- Using your multimeter, test the fuses in the fuse box to find a switched fuse. Set the multimeter to DC voltage. With the ignition off, touch the probes of the multimeter to the two test points on top of each fuse. There should be no voltage reading. Now, turn the ignition to the "on" or "accessory" position and repeat the test. A switched fuse will show a voltage reading (approximately 12V) with the ignition on and no voltage with the ignition off. Commonly used switched fuses are for the radio, wipers, or other accessories.
- Important! Choose a fuse with a similar amperage rating to the cigarette lighter fuse. This ensures the circuit is properly protected. If you can't find one with a similar rating, choose one with a slightly higher rating, but never lower.
Disconnect the Cigarette Lighter Wiring:
- Locate the wiring connected to the back of the cigarette lighter socket. This usually involves removing some trim panels around the center console or dashboard. Disconnect the positive wire (usually red) from the socket. Note the color of the wire and its connection point.
Connect the Fuse Tap:
- Insert the fuse tap into the switched fuse location you identified earlier. The fuse tap allows you to add a new circuit without cutting into the existing wiring. It typically includes two fuse slots: one for the original fuse and one for the new circuit.
Run New Wiring:
- Run a length of new wire from the fuse tap to the back of the cigarette lighter socket. Use wire strippers to expose the ends of the wire and crimp or solder a connector onto one end to connect to the fuse tap. Crimp or solder another connector onto the other end to connect to the cigarette lighter socket.
- Connect the wire from the fuse tap to the positive terminal on the back of the cigarette lighter socket where you disconnected the original wire. Make sure the connection is secure.
- Grounding: Ensure the cigarette lighter socket has a good ground connection. The original ground wire (usually black) should remain connected to the socket's ground terminal. If necessary, clean the ground connection point to ensure good conductivity.
Test and Secure:
- Reconnect the negative terminal of the battery. Turn the ignition on and check if the cigarette lighter/power outlet is working. Then, turn the ignition off and verify that the outlet is no longer powered.
- If everything works correctly, secure the wiring with zip ties or electrical tape to prevent it from getting pinched or damaged. Reinstall any trim panels you removed.

Common Issues and Maintenance Concerns

Blown Fuses: If the cigarette lighter/power outlet stops working after the modification, check the fuses. A blown fuse indicates an overload or short circuit. Replace the blown fuse with one of the same amperage rating.
Loose Connections: Loose connections can cause intermittent problems or prevent the outlet from working altogether. Periodically check the connections at the fuse tap and the cigarette lighter socket to ensure they are secure.
Wire Gauge: Using too thin of a wire can cause overheating and voltage drop. Make sure to use wire that is rated for the current draw of the cigarette lighter socket and any devices you plan to plug into it. 16 or 14 gauge automotive wire is typically sufficient.
Poor Ground Connection: A poor ground connection can cause the outlet to malfunction or not work at all. Ensure the ground connection is clean and secure.

Do's and Don'ts / Best Practices

Do's:

DO disconnect the negative terminal of the battery before starting any electrical work.
DO use a multimeter to identify switched and unswitched circuits.
DO use a fuse tap (add-a-circuit) to safely add a new circuit to the fuse box.
DO use appropriate wire gauge for the current draw of the circuit.
DO secure all wiring with zip ties or electrical tape to prevent damage.
DO test the circuit thoroughly after completing the modification.
DO consult your car's wiring diagram if you're unsure about anything.

Don'ts:

DON'T cut into the existing wiring. Use a fuse tap instead.
DON'T use a fuse with a lower amperage rating than the original fuse.
DON'T overload the circuit by plugging in too many high-power devices.
DON'T skip disconnecting the battery – safety first!
DON'T guess. If you're not sure about something, consult a qualified mechanic.
DON'T leave bare wires exposed. Always use connectors or insulate with electrical tape.

Conclusion

Modifying your cigarette lighter socket to turn off with the car is a relatively straightforward project that can save you from potential battery drain. By carefully following these steps and taking the necessary precautions, you can successfully reroute the power supply and enjoy the convenience of a switched accessory outlet. However, if you're not comfortable working with electrical systems, it's always best to consult a qualified mechanic. A wiring mistake can lead to serious damage to your car's electrical system. With patience, careful planning, and the right tools, you'll be cruising with peace of mind knowing your battery won't be drained by a forgotten phone charger!