A loose, dirty, or poorly-crimped connection can develop a significant amount of heat without exceeding the current capacity of a fuse. Installing a fuse way above the current carrying capacity of the wire involved can also lead to overheating, such as using a 30 amp fuse on an 18 gauge wire, for instance. Fuses are supposed to protect wires, not the end item in the circuit. It sounds like you need to find a better electrician, before this guy burns your truck down!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!