Rally Pac Installation on 1964-1966 Mustangs | Mustang The following are diagrams on how to install a Rally Pac into your 1964-1966 Mustang. Click on a picture to get a bigger view. 1964-66 Ford Mustang rally pac, clock, tachometer parts. 1964-66 Rally Pac Wiring Harness Under Dash. 1964-1966 Ford Mustang Rally Pac under dash wiring. Harness that plugs into main under dash harness. This harness must be used when installing a Rally Pac. $28. Add to Cart Compare. Quick view. 1965 Rally Pac Clock Lens. 1965 Ford Mustang rally pac clock lens.