When applying decals, you want an absolute “squeaky clean”, literally. Wax, chemicals and more can create a barrier between the vehicle and the adhesive on your decals. While they will stay put for a little while, in the long run, you will see your decals fail, no matter how great a quality. Your decal quality is only as good as the prep job. Here I have cleaned off one area with wax remover, soapy water and Isopropyl. The other area just soapy water and Isopropyl. You want to hear a squeak!