Chevy Metro melting wire when starting engine - HELP

I have a 1998 Chevy Metro, 3cyl, 1.0 with mileage: 115,000. When starting the engine there is an intermittent problem with the ground wire from the ignition coil to the engine block getting hot and melting the plastic insulation. When this happens the engine will not start. I have disconnected the air conditioning fan wire (No AC anyway) and replaced the ignition coil. Normally the car starts fine but every once and awhile this problem still occurs on a random basis. I have temporarily replaced the ground wire with one of heavier gauge copper. When I replace the wire I can usually start the car and the problem disappears, until the next time. It seems to be more frequent when first starting the car in the morning. Please help me with this strange problem. Thanks