2003 Lexus RX300 non function break lights. Replaced the stop lights actuator already

Question

2003 Lexus RX300 rear break lights do not work. Stop lights actuator replaced already and didn't fix it. I'm not sure if it's the wiring harness. Fuses are functional. Bulbs are all new and functional

Answer 1

Since you've already replaced the stop light switch (actuator), checked the fuses, and confirmed the bulbs are new and functional, there are a few other potential causes for your Lexus RX300's rear brake lights not working. Here’s a step-by-step guide to help narrow down the issue:

1. Check the Brake Light Relay

The 2003 Lexus RX300 is equipped with a brake light relay, which controls the flow of electricity to the brake lights. If this relay is faulty, it can prevent the brake lights from turning on even if the switch and other components are working. You can:

• Test the relay using a multimeter to ensure it clicks and functions properly when power is applied.
• Swap it temporarily with another known working relay of the same type to see if the brake lights come on.

2. Inspect the Wiring Harness

It's possible that there's a break or short in the wiring between the brake switch, relay, and the brake light assembly. Since you suspect the wiring, here’s what you can do:

• Visually inspect the harness for any obvious signs of wear, fraying, or corrosion, especially in areas where the harness passes through metal bodywork (it could get pinched or damaged).
• Use a multimeter to check for continuity between the brake switch and the brake light assembly. You’ll want to trace the circuit from the fuse box to the rear of the vehicle to ensure the wiring is intact.

3. Ground Connections

• If the ground wire for the brake lights is corroded or loose, the circuit will not complete properly. Inspect and clean the ground points for the rear brake lights, usually located near the taillight assemblies or on the frame of the car.

4. Brake Light Socket Issues

• Even though the bulbs are new and functional, the sockets themselves can have issues such as corrosion or poor contact. Check the sockets for any signs of:
  • Corrosion
  • Bent terminals that might not be making proper contact with the bulbs.
• Clean or replace the sockets as necessary.

5. Check for Aftermarket Electrical Components

• If there are any aftermarket components, like a trailer wiring harness, connected to the brake light circuit, it could be causing issues. Sometimes, poorly installed or damaged aftermarket wiring can interrupt the brake light circuit.

Next Steps:

• If you have access to a scan tool, you might be able to check for any body control module (BCM) faults. Sometimes, modern cars with complex lighting systems will have BCM-related faults that could prevent certain lights from working.

If these steps don't resolve the issue, the problem might be a deeper wiring harness fault, which would require tracing the wires or using a more advanced diagnostic tool to pinpoint the problem.