the TF trucks have the same circuit breaker in the headlight switch. This is designed to allow a reset after the overload situation is resolved so the headlights will be restored.
Actually high resistance does not lead to open bimetallic contact points. Over current through the bimetallic strip, which occurs due to low resistance such as a short circuit or too many loads, does that. Dirty contacts, bad grounds, corrosion, etc., won't blow a fuse or trip a breaker. A high voltage drop occurs in these cases which naturally limits current and results in dim or no lights in a lamp circuit or no operation at all on other systems.
