Wrong Alternator?

domdart said

I have the voltage regulator for the round alternator, so they match. My harness has the ring connector and the single green wire. I searched the forum and learned that others have gone thru a few reman alternators.

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The only way to use the one on the right (with two insulated field terminals) with the voltage regulator and wiring on your '68 is to connect one of the two terminals to ground. That's how the circuit through the rotor is completed.
There were also roundback versions with two insulated terminals (1970-71). I bought one from a junkyard when the bearing siezed on the one in the car.
Did this at a friends house using what her dad had on hand. It still works fine. Its on my shelf as a backup.