What should be done to prevent contamination of a vehicle surface before painting?

Washing and drying the surface properly is crucial to preventing contamination before painting a vehicle. Contaminants such as dirt, grease, wax, and oils can inhibit paint adhesion, leading to surface imperfections, peeling, or a poor finish. By thoroughly cleaning the surface, you ensure that these unwanted substances are removed, allowing the paint to bond correctly with the vehicle's surface.

Proper washing should include using appropriate cleaning agents and techniques to ensure that all areas are covered. After washing, drying the surface is equally important to prevent water spots and ensure that the paint adheres smoothly.

The other options do not effectively address contamination prevention. For instance, using thinner around the edges could introduce additional contaminants or solvents that might affect paint adherence. Painting in a dimly lit area is unadvisable, as it prevents the painter from seeing surface imperfections or contaminants clearly that may need to be addressed. Applying primer only without proper cleaning may create an even worse situation, as priming over a contaminated surface will likely lead to defects in the finish. Proper cleaning is thus the foundational step in preparing a vehicle surface for painting.