1. Bulbs:
* Burned-out brake light bulbs: This is the most common cause. Check all brake light bulbs (both sides). Even if one filament is working (for the tail light), the other (brake light) might be burnt out. Replace any that are faulty.
2. Fuses:
* Blown brake light fuse: Check your owner's manual for the location of the fuse box(es) and the correct fuse for the brake lights. A blown fuse will interrupt power to the entire brake light circuit.
3. Brake Light Switch:
* Faulty brake light switch: This switch is located near the brake pedal and activates the brake lights when the pedal is depressed. A faulty switch can fail to close the circuit, preventing the lights from coming on. This is a very common cause of brake light failure.
4. Wiring:
* Broken or corroded wires: Check the wiring harness leading to the brake lights for any breaks, corrosion, or loose connections. Focus on the area around the brake pedal and the taillights themselves. Rodents can also cause damage to wiring.
* Poor ground connection: A poor ground connection can prevent the circuit from completing, causing the lights not to illuminate. Check the ground points near the taillights and elsewhere in the circuit.
5. Brake Pedal Position Sensor (if equipped):
* Malfunctioning sensor: Some vehicles use a sensor to detect brake pedal position in conjunction with or instead of a brake light switch. A malfunctioning sensor can prevent the brake lights from illuminating.
6. Trailer Wiring (if applicable):
* Trailer wiring short circuit: If you regularly tow, a short circuit in your trailer wiring could draw down power, preventing the truck's brake lights from functioning. Disconnect the trailer and test again.
7. Body Control Module (BCM):
* BCM malfunction: While less likely, a problem with the Body Control Module could cause this issue. The BCM controls many electrical functions, and a fault could cause specific circuits to fail. This usually requires professional diagnosis.
Troubleshooting Steps:
1. Check the bulbs first! This is the easiest and cheapest fix.
2. Check the fuses. This is a quick and easy check that could save you a lot of time.
3. Inspect the brake light switch. This is usually accessible without too much difficulty. You can test it with a multimeter if you're comfortable doing so.
4. Visually inspect the wiring harness. Look for any obvious damage.
5. Test the ground connections. Ensure they are clean and tight.
6. If you frequently tow, disconnect the trailer.
If you've checked all of the above and the problem persists, it's best to take your Ford F-350 to a qualified mechanic for diagnosis. They'll have the tools and expertise to pinpoint the exact cause and perform the necessary repair. Remember safety first – don't drive with malfunctioning brake lights.
