With any paint job, the final finish and durability will be determined by how well you prepped the surface. You will need to ask yourself a few questions before you dive into your project. Do you plan on stripping the vehicle to bare metal or painting over the existing finish? Stripping the vehicle to bare metal allows you to see what is hiding under the paint - rust, body filler, shoddy repairs, and other damage. You'd be surprised what has been found under existing layers of paint. Stripping the vehicle to bare metal also allows you to know exactly what products are being used. If you paint over an existing finish (this is perfectly acceptable for some applications), you never really know what is hiding under the surface. Also, if this finish was not properly prepped for, your new coating may flake off due to the existing finish flaking off. If you do not know the history of the finish on the vehicle, it is generally a better idea to strip it to bare metal and start fresh. There is nothing worse than having a new paint job flake off or have rust start popping out due to shoddy repairs that were made under an existing finish.
When painting over an existing finish, the finish must be in good shape. Faded finishes are okay, but it should not be peeling, cracked, or otherwise damaged. If the vehicle has been repainted, it is recommended that you strip the vehicle down and start from bare metal. If you do decide to paint over the existing finish, wash the vehicle and then use a quality wax and grease remover on the surface. This will remove any wax that could cause adhesion problems. For this project we simply scuffed the panel with a medium scuff pad to give the primer something to bite into.
here for a complete list of Eastwood's Clears & Primers