You may be over thinking this issue which might not be overload, especially if the fuse itself didn't blow. The heat generated which melted the holder is likely to be due to a localised resistance in the fuse holder itself, due in turn to dirty contacts. This would cause a volt drop proportional to the total current draw of the circuit and according to Ohms law. The resulting power loss would he dissipated as heat and a significant amount if the current draw was high. I know you said a replacement fuse got you going again but that might be just remaking the dirty contacts so likely only a temporary cure.

Suggest a thorough clean of contacts if the fuse holder is still serviceable. Check also for water ingress which may have corroded contacts.

Last edited by Richard Wood; 20/11/20 10:19 PM.

Richard

2018 Roadster - Red/Magnolia - "Morton"
1966 Land Rover series 2a SWB
1960 Velocette Venom