* Brake Light Switch: This is the most common culprit. The switch is located on the brake pedal assembly and activates when you press the brake pedal. It's a relatively inexpensive and easy part to replace. Test it with a multimeter to see if it's making proper contact when the brake is pressed.
* Wiring: Check the wiring from the brake light switch to the brake lights themselves. Look for broken wires, corroded connections, or loose terminals. Pay particular attention to the wiring harness near the brake pedal and near the taillights. A visual inspection is crucial, but you may also need a multimeter to check for continuity.
* Bulbs: While you've likely checked this already, make sure both brake light bulbs are good. Sometimes a bulb can appear fine but be intermittently faulty or have a broken filament that only fails under pressure.
* Tail Light Socket/Connectors: The connectors at the taillights themselves can corrode or become loose. Carefully inspect the sockets and clean any corrosion. Make sure the bulbs are seated correctly in the sockets.
* Ground: A poor ground connection can prevent the brake lights from working. Locate the ground wire(s) for the taillights and ensure they are clean and securely connected to a good ground point.
* Multi-function Switch (Column Switch): Less likely, but possible. This switch controls various functions, including turn signals and possibly brake lights depending on the wiring setup. A faulty switch can cause intermittent or complete brake light failure.
Troubleshooting Steps:
1. Visual Inspection: Carefully examine all the wiring, connectors, and bulbs.
2. Test the Brake Light Switch: Use a multimeter to check the continuity of the switch when the brake pedal is pressed.
3. Test the Bulbs: Replace them with new ones, even if the old ones *seem* okay.
4. Check the Wiring: Use a multimeter to trace the wiring from the switch to the taillights, checking for continuity at each point.
5. Check the Ground: Clean and tighten ground connections.
6. If all else fails: Consult a wiring diagram specific to your 1976 Monte Carlo. This will help you systematically trace the circuit.
Remember safety first! Disconnect the negative battery cable before working on any electrical components in your car. If you're not comfortable working with car electrical systems, it's best to take your Monte Carlo to a qualified mechanic.
