It was used for RPO Z22 (Rally Sport). In 1967, it was used for the power wire that came from the headlight harness to the ignition and light switch, and for 1968 and 1969 it was used for the vacuum hoses.
As shown in the various assembly manuals, for 1967, see UPC Z22, Sheet B8, View A, for 1968, see UPC 0, Sheet A8.5, Item 6, and for 1969, see UPC 0, Sheet A9, Item 7.
Ed