Just to let you know, my early '67 GT 500 had a separate wire that was covered with a braided cover. It it is taped about every 14" to the tail lamp harness. My original was used by Alloy Metal Products to make the trunk lamp wiring, not to mention the right side fastback courtesy lamp harness. -Keith
My March SJ Shelby has a separate wire, but no covering at all! Its insulation is thicker than it needs to be so I surmise the thicker insulation is in lieu of the separate cover. And mine was taped every 36" (approx). However, rather than using standard 3/4" friction tape, it uses 1 1/2" friction tape.
I'm getting it ready to be recovered by Rhode Island Wire.