My brother had a not dissimilar problem with another Fiat product of not dissimilar vintage in the mid 60’s.

He had then a Fiat 500 that had a thick cable connected to the starter terminal via a tag together with a lighter cable on the same terminal. He was having intermittent starting problems and found that moving the cables on that terminal enabled the car to be started, but it wasn’t ideal, so disconnected them to give them a clean. This action served its purpose, no more starting problems.

A few days later, he embarked on a weeks trip from Wolverhampton to the Isle of Skye and back, which went well until he reached some 9 miles from home when it stopped and yours truly was called out to rescue. Close inspection found that during reassembly the smaller wire had not been reattached and therefore the battery had not been charged and was flat. My brother was not over mechanically minded, a lucky round trip!!