I did run across this at some point when I was wondering the same thing. Did not really say exactly what the T/O means unless like stated above.
The abbreviation T/O is used in the component location section to indicate a point in which the wiring harness branches out to a component.
Upon a little further digging I did find a document that stated what Bill said above exactly.
Eddie,
81 F100 Custom SWB, 5.0L, 4x2, Single Rail Four-Speed Overdrive, 3.00 Non-Limited Slip Rear Axle, Non A/C truck to complete 85 F150 factory A/C conversion, Nutmeg interior color.