The tilt wheel installation is documented in the "1968 Mustang Chassis Assembly Manual" (AM0025) page 68 (it also includes Cougar). The underdash electric wiring harnesses are covered in the "1968 Mustang Electric Assembly Manual" (AM0023) page 34 (E8-8600-1).
Jim
Note: There are a couple of errors on the 1968 chassis installation page (AM0025, pg 68). Ford Car Parts (75 edition, aka MPC) Illustration Sect 35 page 11 (available in this forums' library) has a lot (yes, it is two words) of details, but it may not be what was used on the assembly line.