The MSD is an add-on system. You don't have to replace anything. On my truck I bought the optional harness so hook-up was a breeze (1/2 to 1 hour depending on how picky you are). It'd be a breeze without the harness. Hardest part was finding a spot under the hood for the new MSD box so it looked, "nice-n-purty." I really like the system. Good bang for the buck and NOWHERE near as hard as installing headers.

Randy