I emailed Painless to find out if they where going to be making a 67/68 Mustang wiring harness any time soon (they already have a 65/66). Here's their reply:
We have a harness in R&D. We are expecting to release this harness at the SEMA show in November. start looking for it to be on the market by mid
October.
Painless Wiring is an aftermarket company that makes wiring harnesses for specific cars and universal kits for hot rods. They offer everything from fuse blocks with extra spaces to upgraded wiring for headlights using relays. There wire is a heavier duty type than what one would usually find.