Brake Light Circuits
Brake light circuits are parallel circuits. In a parallel circuit, one bulb can burn out, and the other bulbs still function normally. If brake lights were wired in a series circuit, when one bulb fails, the other bulbs would also fail to light. If one bulb out in a brake circuit, it is likely associated with that individual bulb or the socket.
Each item added to a parallel circuit decreases the resistance in the circuit. This addition increases the current. Current flows through all of the bulbs regardless of their resistance. Remember Ohm's Law (I=V/R) when 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.