Dead giveaway for fuse box problems

A thermal camera or temperature gun can be used to identify problems like that. Temperature guns are inexpensive, but may require stick-on black targets to get around emissivity errors.

The original fuse box contacts are often corroded steel, with original tin or cadmium plating gone. I think there might be replacement contacts available, seems like early Mustangs used similar.

I have considered designing a replacement PCB, with heavy copper traces, copper buses, and sockets for modern blade fuses. There could be other improved features, including relays. Right now many irons in the fire.