I banged my head against the wall for two days straight trying to figure this out on a friend of mine's car. We even swapped the alternator itself, and that didn't change anything. It isn't ground related, it has to do with the initial charge the alternator takes to get started. The alternator takes a little bit of power from the battery to "activate" the magnetic field. The only idea I could come with was to run a wire straight from the battery to that connector on the alternator. I can't remember off of the head exactly where on the alternator you need to put that wire, I'll have to poke my head under my hood later to figure it out. The problem is, I wasn't ever able to test this idea out as we gave up working on his car. He had to rev over 4k to get the alternator to kick on. His radar detector had a voltmeter in it. It was interesting to watch the voltage. the motor would start and the voltage would be 10-11 and would slowly drop as you drove it. the moment you hit 4k, the voltage would shoot right up to 14.5+ and not have any issues until the engine was shut off.