Inspect the terminals, they must be bad and also inspect earth wire it must be cracked and out of order now. Try to change the terminals and put a new heavy gauge negative wire with both ends clamped with lugs that can be tightened into terminals with nuts. THe car will start in half self. Also make sure the positive wire is also in good spec if not change it. THe wire terminal on the starter should be in good nick, put some grease in the protective plug and put it on the nut of the starter motor where the positive wire is clamped.