A circuit breaker is a protective device designed to open a circuit when a current load is in excess of rated breaker capacity. If there is a short or other type of overload condition in the circuit, the excessive current will open the circuit between the circuit breaker terminals. There are two types of circuit breakers used in GM vehicles: cycling and non-cycling.
The cycling circuit breaker will open due to heat generated when excessive current passes through it for a period of time. Once the circuit breaker cools, it will close again after a few seconds. If the cause of the high current is still present, it will open again. It will continue to cycle open and closed until the condition causing the high current is removed.
There are two types of non-cycling breakers. One type is mechanical and is nearly the same as a cycling breaker. The difference is a small heater wire within the non-cycling circuit breaker. This wire provides enough heat to keep the bimetallic open until the current source is removed.
The other type is solid state, called an Electronic Circuit Breaker (ECB). This device has a Positive Temperature Coefficient. It increases its resistance greatly when excessive current passes through it. The excessive current heats the ECB. As it heats, its resistance increases, therefore having a Positive Temperature Coefficient. Eventually the resistance gets so high that the circuit is opened, removing voltage from its terminals. Once voltage is removed, the circuit breaker will re-close within a second or two.
The primary application of a circuit breaker is the headlights. If the headlamps were protected by a fuse and fault developed driving at night, the headlamps would go out, an unacceptable situation. So a cycling-type circuit breaker is built into the headlamp switch. If a fault develops, the headlamps will go our momentarily, then the breaker quickly resets and the headlamps will come on again. If the fault is still there, the headlamps will go out, the breaker will reset again, and the headlamp will come on again. If the cycle keeps repeating, the result is the headlamps will seem to continuously flash on and off. This at least allows the driver to safely stop the vehicle.
The windshield wiper motor is also protected by a circuit breaker. If the wiper motor overheats (wipers frozen to the windshield or stuck in heavy snow, stalling the motor, for example) the circuit breaker will trip, remaining off until the motor cools or the overload is removed.
There may also be some circuit breakers in the fuse box for the power door locks, power seats and power windows.