* Brake Light Switch: This is the most common culprit. The switch, located on the brake pedal, is a mechanical device that closes a circuit when the brake pedal is depressed. It can wear out, become misaligned, or get jammed, preventing the circuit from closing. Even though the switch might *look* okay, it could be internally faulty.
* Wiring Issues: A break in the wiring harness between the brake light switch and the lights themselves is possible. This could be a damaged wire, a corroded connection, or a poor connection at a splice. Check the wires carefully for breaks, fraying, or corrosion, particularly near the brake pedal and at the tail light assemblies. These vehicles are known for wiring issues around the chassis.
* Brake Light Bulbs: Though you might think this is obvious, a burned-out bulb *could* be the issue even if it doesn't *look* burned out. Sometimes the filament breaks internally and only appears fine from the outside. Test all brake light bulbs to be sure.
* Grounding Issues: A poor ground connection can prevent the brake lights from working. The ground wire needs to provide a complete circuit for the current to flow. Inspect the ground wires at both the brake light switch and the tail light assemblies. Corrosion or loose connections are common causes of grounding problems.
* Central Electrical Control Module (or similar): On some vehicles, especially older ones, there might be a central module that controls various electrical functions. A malfunctioning module could be disrupting the brake light circuit even if other electrics are working fine. This is less likely, but possible.
* Faulty Brake Light Circuit: A short in the brake light circuit itself is less common but could be causing the lights to malfunction without blowing the fuse. This usually results in other electrical issues though.
Troubleshooting Steps:
1. Check the bulbs: Replace all brake light bulbs as a starting point.
2. Test the Brake Light Switch: With a multimeter, check for continuity across the switch terminals when the brake pedal is depressed. If no continuity, the switch is faulty.
3. Inspect the Wiring: Visually examine all wiring between the switch and the tail lights for damage, corrosion, or loose connections. Pay attention to the areas prone to movement or abrasion.
4. Check the Ground Connections: Clean and tighten all ground connections related to the brake lights.
5. Use a test light: A test light can be used to trace the circuit and identify where the break in the circuit lies.
If you're not comfortable working with car electrics, take your Transit to a qualified mechanic for diagnosis and repair. It's safer and can save you time and potential damage.
