Is interesting that givdrver has to hold the key at start for a few seconds before the engine cranks over.
Which is another indicator of a high-resistance joint!...connection made, current flows through poor connection , which heats up, arcs over and"welds" a connection, or simply expands with heat, tightening the contact and increasing the area sufficiently to carry the required current.
A tight joint is not necessarily sound electrically.......way back in the 60's an engineering lecturer from the Generating Board, said they'd tried multistrand aluminium cables without success. no matter how they tried to clamp the ends, a lot of the strands made poor contact.
Aluminium oxidises instantly on contact with air- even that freshly-polished vintage plane has a film of oxide!