From that picture it looks like the black and green wires from the internal regulator on the alternator were disconnected, and wires from the new wiring harness were connected?
Make sure the battery is fully charged, it it is low, it may charge at a higher voltage for a few minutes, but 16.5 sounds too high?
I would start by disconnecting both wires from the alternator field connections and make sure the alternator is not charging. Then I think the blue wire should have +12 volts when the key is on. Connect that back up and if the alternator starts charging at 16+ volts, it might indicate the other field connection is shorting to ground. Disconnect the voltage regulator plug at the firewall voltage regulator, and ohm it out to make sure it is not shorted. If it is not shorted, connect it to the alternator field connection. With the key on the two sockets in the voltage regulator should have +12 volts (disconnected from the regulator.) Connect to the regulator and start the car and check the charging voltage.
One last check before replacing the voltage regulator is to run a separate ground wire from the engine to the regulator case in case the VR ground reference is not the same as the engine?