Tail Lights Stay On When Car Is Off - Common Causes & Solutions

Just like other car lights, including the brake and headlights, your vehicle’s tail lights are susceptible to various problems. But what are these issues, you ask? One common problem is the lights failing to turn off after switching off your car’s ignition.

Unfortunately, there are many reasons this may happen. And if these causes are not fixed, the lights may drain the battery. Nothing to worry about, though!

In this guide, we will explore the causes of the tail lights staying on when the car is shut off. We will also discuss the different solutions available.

Why Do Tail Lights Stay On When Car Is Off?

The common causes of tail lights staying on even when your car is off include the following:

A stuck-on tail light or lamp relay
Bad trailer plug connector
Defective brake light switch
Weak or shorted ground wire
Corroded tail light wiring harness

Without further ado, let’s discuss these causes in detail, including their solutions.

Tail Light Relay Stuck On

Your vehicle’s tail lights work on a relay linked to the headlight system. When you turn on the headlights, the relay usually channels electric power to the tail lamps.

These lights are timed and will stay on for up to 45 seconds before going off. However, if the relay is stuck on, power will intermittently flow to the tail lamps. As such, the tail lights will stay on when your car is off.

Solution

The only solution here is to replace the tail lamp relay(our pick). Below is how to do the replacement.

Step 1: Locate the relay in the main fuse box under the hood. But in some vehicles, it could be integrated into your car’s lightning control module.
Step 2: Unhook the negative battery cable.
Step 3: Disconnect the old relay from the fuse box.
Step 4: Install the new relay.
Step 5: Hook the negative battery cable back and test the lights.

Bad Trailer Plug Wiring Connector

The trailer plug of your truck is designed to supply electrical power to your trailer or camper’s brake and lighting system. When the wiring of your vehicle’s trailer plug becomes defective, there may still be a bit of current moving in the circuit.

As such, when all the lights are off, including the car, the taillights may still get power from the trailer plug.

Watch this video of a Chevy truck with tail lights staying on problem when the car is off:

Solution

To fix this problem, you must install a new trailer plug connector(Our pick). Here is how to do the replacement.

Step 1: Locate the trailer plug connector at the rear of your truck, in the rear bumper. It is near the hitch and the tail lights.
Step 2: Unplug the trailer wiring harness from the plug.
Step 3: Unfasten the screws securing the connector to the trailer hitch.
Step 4: Clean the plug using an electric contact cleaner and apply some dielectric grease on the small holes.
Step 5: Install the new trailer plug connector using new bolts and check if the tail lights are off.

Defective Brake Light Switch

The brake light switch is designed to activate the brake lights when you step on the brakes. This is by transmitting electrical signals to the brake light system. The signal also triggers the tail lights to turn on in some cars.

Unfortunately, a defective brake light switch may sometimes get stuck in the “ on” position. And when this happens, the brake lights and the tail lights may stay on even when the car is off.

Solution

The short-term solution would be disconnecting the battery whenever you remove the key from the ignition. Or, you could readjust the switch. However, the long-term solution is to replace the brake light switch. Check out how to do it.

Step 1: Locate the brake light switch under the dashboard beside the brake pedal.
Step 2: Unplug the switch and check if the lights are off.
Step 3: If the tail lights go off, unscrew the mounting nuts that secure the brake switch and remove the switch.
Step 4: Install the new brake light switch and secure it with the mounting screws.

Weak or Shorted Ground Wire

Turning off the headlights usually breaks the circuit, causing the tail lights to turn off. However, if there is a short in the ground wire, this may create another path for electric power to flow. This path may bypass the headlight switch, keeping the tail lamps on even when the car is off.

Generally, a weak electrical grounding may be due to damaged wiring, corrosion, or loose connections. So, you must check your vehicle’s ground wires near the tail light.

Solution

Below are steps to fix a weak or shorted ground wire in your car.

Step 1: Disconnect the battery’s negative cable.
Step 2: Get a multimeter and set it to resistance mode.
Step 3: Place the multimeter’s probes into your car’s negative battery cable and the other one on your vehicle’s metal chassis.
Step 4: Check the reading. If you get a reading of 1 or OL, the ground wire has a short circuit. OL means open loop, overload, or the circuit is incomplete.
Step 5: Cut the damaged ground and strip a section on both ends of the remaining wire.
Step 6: Get a new ground wire to replace the one you have cut.
Step 7: Use terminal connectors to connect the new wire to the existing one. Then, use electrical tape to insulate any exposed wires.

Corroded Tail Light Wiring Harness

Your vehicle’s tail light harness comprises an assortment of electrical wiring and sockets designed to keep the tail lamps illuminated.

If the wiring harness is corroded, it may pull power from another circuit. And when this happens, the electric power will still flow to the tail lights causing them to stay on even when the car is off.

Solution

It would be best to clean the wiring harness to remove the corrosion build-up on the wires. This is how you do it:

Step 1: Find the wiring harness connected to the taillights in the rear of your car.
Step 2: Disconnect the wiring from the tail light assembly.
Step 3: Use a wire brush and electrical contact cleaner to remove the corrosion on the wires.
Step 4: Apply dielectric grease (our recommendation) to the wires to protect them from more corrosion.
Step 5: Reinstall the wiring harness on the tail light assembly and test the connection.

Frequently Asked Questions [FAQs]

In this section, we will respond to some frequently asked questions regarding tail lights staying on when the car is off.

Can tail lights drain the battery if they stay on when the car is off?

Yes. If left indefinitely, the tail lights can drain your battery. This is because these tail lamps are wired right to the battery and connected to the headlights.

Is it expensive to troubleshoot tail lights that stay on?

No. For example, a replacement brake light switch may cost you an average of $16 – $21 for parts alone. Similarly, replacing a tail light relay may cost you between $8 and $15 if you do the replacement yourself.

Conclusion

When you remove the ignition key, your vehicle’s tail lights should turn off. But, sometimes, the opposite may happen: tail lights stay on. This may sometimes happen when the tail light relay is stuck on, or the trailer plug connector is damaged. A ground wire short and a corroded wiring harness may also cause the tail lights to stay on when the car is off.

Fortunately, it is easy to troubleshoot a tail lamp that remains on when the vehicle is off. For example, you could replace the tail lamp relay, brake light switch, and trailer plug connector. Also, cleaning any corrosion build-up on the wiring harness may fix the problem.

Tail Lights Stay On When Car Is Off – Common Causes & Solutions