On the firewall, driver's side above the steering column:
IMG_8417_EDIT.jpg
This is the tag (I know, I need to clean it!)
IMG_8420_edit.jpg
The wiring appears to be military by the tags and the original-looking harness; it is not shown in the pics I've seen of the 100 amp alternator (which my truck has) nor does it appear to be in the electrical diagram in the manuals.
If you click on the individual pictures, they open in a new window, full-screen.
Any help will be very much appreciated!
Best,
-Ken