A healthy electrical system depends a lot on the condition of the main fuse box and fuses.
Torpedo fuses used on classic cars tend to form galvanic corrosion on fuse box terminals. That is more frequent if fuses installed are made of dissimilar alloys (aluminium) than fuse box post, but it is non exclusive to them as I have seen also that problem with brass filament fuses.
Time does not forgive any component on our classic, therefore it is very important to replace fuses even when they are not burned to assure good conductivity; and of course to fine sand the main fuse box terminals at the same time you complete previous action.
Any competent wiring harness restoration should pay extreme attention to this electrical system component to reach peak quality levels.