Is the port where the cable connects to the GPS loose at all It could be an issue of broken solder joints at the port and if you wiggle the wires around you get a connection . Inspect the port for how well it connects look closely inside the port forr lint or dirt and if you do need to clean the port use a toothpick are plastic pick . Dont use metal as it can break the port. Next check your cable as well could be a problem your new cable . How long will you GPS run without being plugged in , it may need a new battery. This guild will help with replacing the battery
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Hope this helps