Hello: New here.
Struggling for ages to figure out where the 'I' regulator wire goes between my regulator and the alternator. I understand It runs from the regulator to a light bulb that turns on only during start up and then shuts off and I believe the other end goes to the ignition.

But where on the ignition ? Something about the positive side of the coil ? I just can't sort out this one wire so my battery never charges.

My factory harness is long gone and I just have an octopus of wires under the dash.

Any assistance is appreciated. It is a 3 wire, 1G alternator.

 

Attached is a wiring diagram that may help. The firewall main disconnect the ignition wires go through is the one closest to the center of the car. There is no charging light on a '66, there is a gage. Regardless, the wires coming from the alternator all go through a 3 pin connector. One is ground, one goes to the battery side of the starter solenoid, and the last goes to the regulator. The one that goes to the starter side of the solenoid is spliced to the wire I think you're interested in, which is #37 (black yellow) going into the bulkhead disconnect and changing to #654 (yellow) from the disconnect (under the dash).

 

Thank you Mustang66