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I don't understand the triangles and page numbers. ...
Generally speaking they are off-page references. That doesn't mean they're all correct, of course....
So if you consider triangle D on page 1 you'll find the "other end" of that wire as another triangle D on page 4, middle left, next to the "A/C Switch".
In the case of your triangle "I" you find the corresponding triangle I on page 10 of the schematics (not the manual page #; manual page is schematic page plus 38) at the lower right where there is a drawing of the back of the recirc switch. This is a somewhat unconventional way to draw an electrical diagram. Usually you draw switches in there "logical" form like they do with the brake switch on page 3. Then usually you have a separate drawing of each switch identifying terminal number and their physical location on the switch. This drawing combines the two, sort of, with certain switches that are drawn physically after the more conventional diagrams but also showing their connection into the preceding schematic diagrams.
Page 1 is the page with the battery, alternator, ignition switch and starter on it. That's where you'll find the other end (in this case the current source) of triangles A and C, although both A and C are "multi-point" that is they show up in several places. This just means all those "A"s are connected to all the other "A"s, etc.
BTW the wire colors are there; look for one or two letter codes, and look up the corresponding color from the table at the upper right of page "zero" (of what Rick sent) or page 38 of the manual. And BTW the number next to those color codes is the wire size in square millimeters.