BUSSMANN 20AMP 12V Resettable Blade Fuse Circuit Breaker Manual Reset
Replaces standard blade fuse. If you overload the circuit or have an electrical short these circuit breakers simply open to prevent the current flow.
If circuit breaker is tripped, press the BLACK reset button. This is the same as replacing an old fuse.
This is a much safer option than increasing the fuse rating that many people do or continuing to burn out fuses until they find the problem.