1. Brake Pedal Switch (Brake Light Switch):
* Problem: This switch is the most common culprit. It's a relatively inexpensive part and it's possible it's failing intermittently, causing the delay. The trailer brake controller likely bypasses this switch, using its own separate power and ground to activate the lights.
* Troubleshooting: You should carefully inspect the brake pedal switch. It might be worn, dirty, or have a loose connection. You can try cleaning the contacts or replacing the switch entirely. This is often a relatively easy DIY repair.
2. Grounding Issues:
* Problem: A poor ground connection for the brake light circuit can cause delays or prevent lights from working altogether. Corrosion or a loose connection at any point in the ground wire can be the cause.
* Troubleshooting: Trace the ground wire from the brake light circuit. Look for corrosion or loose connections at the connection points on the body, chassis, or at the light fixtures themselves. Clean and tighten any connections you find.
3. Wiring Harness Issues:
* Problem: Damaged or corroded wires within the brake light wiring harness can create intermittent problems. The trailer brake controller bypasses these issues, since it runs its own wires.
* Troubleshooting: Carefully inspect the wiring harness running from the brake pedal switch to the brake lights. Look for any signs of chafing, damage, corrosion, or loose connections. This will require some patience and potentially tracing wires.
4. Totally Integrated Power Module (TIPM) or Brake Control Module (BCM):
* Problem: While less likely, a problem with the TIPM (if your truck has one) or the BCM could be the source of the delay. These modules control various electrical systems, and a malfunction could cause unusual behavior in the brake lights.
* Troubleshooting: Diagnosing this is more complex and may require professional-level diagnostic tools to check for codes.
5. Third Brake Light Specific Issues:
* Problem: The third brake light might have its own dedicated circuit which is faulty. It could be a bad bulb, a wiring issue specific to that light, or even a relay (though less common).
* Troubleshooting: Check the bulb in the third brake light. Inspect the wiring going to that specific light for damage or corrosion.
Troubleshooting Steps in Order:
1. Check the brake light bulbs: Start with the simplest thing first. Make sure all bulbs are working correctly.
2. Inspect and Clean/Replace the Brake Pedal Switch: This is the most likely culprit.
3. Check the ground connections: Trace the ground wire from the brake lights.
4. Inspect the wiring harness: Carefully examine the wiring for any damage.
5. Use a Test Light or Multimeter: A test light or multimeter will be invaluable in verifying power and ground at various points in the circuit.
Important Considerations:
* Safety: Driving with malfunctioning brake lights is dangerous. If you're unsure about any of these steps, it's best to have a qualified mechanic diagnose and repair the issue.
* Trailer Brake Controller Interaction: The fact that the trailer brake controller works correctly highlights that the issue isn't a complete lack of power to the lights, but rather a problem within the truck's brake light circuit itself.
By systematically going through these steps, you should be able to pinpoint the cause of the brake light problem. Remember safety first, and don't hesitate to seek professional help if you're not comfortable working with car electrical systems.
