Every classic car electrical circuit and the components it serves must be protected by a fuse or circuit breaker. This ensures that if there is a fault in the circuit, it will not result in a ruined component, or worse yet, an electrical fire. But cars built in the 1950s and earlier often do not have the traditional fuse box we’ve come to recognize in more modern cars. Instead, they are often equipped with circuit breakers to protect the circuits.
These circuit breakers protect a series of circuits and are auto-resetting, meaning that once they’re tripped they’ll reset themselves. However, some manufacturers used manually-resettable circuit breakers, usually with a button used to reset them.
This is where enthusiasts get into trouble diagnosing electrical issues as early cars did not have a uniform location for the circuit breakers, and when one trips and stays open, the car owner is left hunting for the circuit breaker location. Sometimes they’re located behind the instrument cluster, or on the firewall behind the dash.
But we’ve seen manufacturers locate them in numerous locations, including under the seat, behind the kick panels, behind the rear seat, in the engine compartment and even in the trunk. Don’t wait to have one fail before to learn the location of your circuit breakers; instead, know where they are and how many amps each is rated for, as it’s always a good idea to keep one in the glove compartment as a spare.
When hunting down the circuit breakers in your car, don’t expect them all to look the same. Commonly in 1930s cars and earlier, these were designed by the manufacturer and would vary in appearance from one make to another. By simply following the electrical circuit from the battery to ground, you’ll discover the location of the breaker.
Fuses and circuit breakers are ‘overcurrent devices’ that are designed to protect your WIRING. I your wiring size is too small or the breaker is rated too high, the wire becomes the fuse. ’50’s Ford headlight switches had a circuit breaker INSIDE the switch for the headlight circuit and glass fuses on the back for brake lights, etc. One of our members complained that his instrument panel was ‘clicking’ and his interior lights were flashing. I told him to feel the harness that feeds the trunk. One of the wires was hot. It ended at his license plate lamps. ‘Makes sense because lamp sockets and plug/receptacles exposed to weather tend to corrode and rust or melt. Use all of your senses when troubleshooting.