Brake Lights

Brake lights are wired in a parallel circuit. One bulb or socket can fail, and the others will still illuminate and function normally. If one light is out in a brake circuit, it is likely associated with the individual bulb or the socket.

A bad stoplight fuse will affect all of the brake lights. The stoplight fuse is designed to protect the circuit from overload. If the stoplight fuse continues to blow, suspect a short to ground somewhere in the circuit.

Remember Ohm's Law (I=V/R) whenever working with automotive circuits. Be careful and check specifications before adding additional items to a factory system. Adding items lowers resistance and increases the current (amperage). This additional current can damage components and burn sensitive wiring.

A series circuit is different. Components are daisy chained and when one bulb fails, the other bulbs are rendered inoperable. A series circuit has one path and current remains the same and voltage is divided among the bulbs. In a parallel circuit voltage remains the same and current is divided among the bulbs. A failed component in a series circuit breaks the circuit causing the other bulbs not to illuminate. In a parallel circuit a failed bulb will not affect the others. They will still function normally.