1. Bulbs:
* Check the bulbs: This is the most common cause. Start by visually inspecting the brake light bulbs in both the taillights. Look for a burnt-out filament. A simple way to check is to turn on your parking lights. If the parking lights work but the brake lights don't, the brake light filament is likely burnt out. If neither work, the bulb is likely bad.
* Replace the bulbs: If a bulb is bad, replace it with the correct type (check your owner's manual or a parts store for the correct wattage and type). Make sure to disconnect the battery negative terminal before working on the electrical system.
2. Fuses:
* Locate the fuse box: Find the fuse box (usually under the dash or in the engine bay – consult your owner's manual).
* Check the fuses: Check the fuses related to the brake lights. They might be labeled, or you might need to consult your owner's manual or a wiring diagram. Look for blown fuses (a broken filament inside). Replace any blown fuses with fuses of the same amperage rating. If a fuse keeps blowing, there's a short circuit somewhere in the system (see step 5).
3. Brake Light Switch:
* Locate the brake light switch: This is typically located on the brake pedal assembly.
* Inspect and test the switch: The switch is a simple mechanical switch that closes when you press the brake pedal. You can test it with a multimeter (set to continuity) by checking for continuity when the brake pedal is pressed. If there's no continuity when pressed, the switch needs replacing.
* Replace the switch: Replacing the brake light switch is relatively straightforward, but you might need to consult a repair manual or online guide for your specific Mustang model.
4. Wiring:
* Check the wiring: Inspect the wiring running from the brake light switch to the taillights. Look for any broken, frayed, or corroded wires. Pay close attention to the connections at the switch, the taillight sockets, and anywhere the wires are routed through potential pinch points.
* Repair or replace wiring: If you find damaged wiring, repair it by splicing in new wire or replace the affected section entirely. Use electrical tape to insulate connections properly.
5. Short Circuit:
* If a fuse keeps blowing: This indicates a short circuit somewhere in the system. This requires more detailed troubleshooting, potentially tracing the wiring with a multimeter to locate the short. A short circuit could be caused by damaged wiring, a grounding issue, or a faulty component.
6. Grounding Issues:
* Check the ground connections: Poor ground connections can prevent the brake lights from working. Inspect the ground connections at the taillights and the brake light switch. Clean and tighten any corroded or loose connections.
Important Considerations:
* Wiring Diagram: A 1966 Mustang wiring diagram is highly recommended. This will show you the exact path of the brake light circuit and help you troubleshoot more effectively. You can find these online or in a repair manual.
* Repair Manual: A shop manual specific to your 1966 Mustang will be invaluable for detailed instructions and diagrams.
* Safety: Disconnect the negative battery terminal before working on any electrical components.
If you're not comfortable working with automotive electrical systems, it's best to take your Mustang to a qualified mechanic. Improper wiring can lead to serious problems.
