On the 1954 Chevrolet truck with a original head light switch.
In the wiring harness, protection is provided for all wiring leading from the light switch by a thermal circuit breaker.
Lighting System, Desciption and Operation Read 2nd paragraph.
The light switch incorporates a 42 ampere
Thermal Circuit Breaker to protect the entire lighting system.
I think you can replace just the Thermal Circuit Breaker if it goes bad.
