Brake Light Circuits
Brake light circuits are parallel circuits. A parallel circuit is used for brake lights because one bulb can burn out, and the other bulbs will still function normally.
If brakes are wired in a series circuit when one bulb fails, other bulbs are rendered inoperable. If one bulb is burned out in a brake circuit, it is likely associated with the individual bulb or the socket. Each item added to a parallel circuit decreases the resistance in the circuit. This increases the current.
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.