2 wire alternator

Longone is right. And it should have a 2 wire alternator.

Look close at your wiring harness the small green alternator wire might be broke off close to the tape (seen this happen before).

Man I wish you would have posted this about 2 days ago. I just switched my 68 over from exactly what you have to the newer dual field system and March serpentine system. If I knew I would have taken pictures of the old system and sent them to you. Bummer.