From Wikipedia: “Project High Wire -
"High Wire" was a modernization program for selected F-100Cs, Ds and Fs. It comprised two modifications: an electrical rewiring upgrade, and a heavy maintenance and IRAN (inspect and repair as necessary) upgrade. Rewiring upgrade operations consisted of replacing old wiring and harnesses with improved maintainable designs. Heavy maintenance and IRAN included new kits, modifications, standardized configurations, repairs, replacements and complete refurbishment.
This project required all new manuals and incremented (i.e. -85 to -86) block numbers. All later production models, especially the F models, included earlier High Wire modifications. New manuals included colored illustrations and had the Roman numeral (I) added after the aircraft number (i.e. T.O. 1F-100D(I)-1S-120, 12 January 1970).
Total production 2,294”