What is the 3" wire connected to, Jerry?

I had a 12v one-wire alternator a few years ago on 12v (conversion) 54 truck with 6-cylinder engine. I do not remember 2 wires being attached (by me) to the alternator (but, my memory on this is very dim. I bought the 1-wire alternator - I did not convert an alternator to 1-wire.

Here is the "wiring" diagram I used - found on the Internet.
Taken from the old web page.