I think that was Dave, not I, with the tail lamp housing cleaning question... but to response to your question/comment I think the vinegar, being a mild acid, would help to remove the dirt and light oxidation on the housings and prepare it for the subsequent steps for polishing and buffing to a clean shiny surface.
Steps from film:
1. Clean the metal with liquid dish soap (1 tsp per cup of hot water); mix until water is soap; scrub with scrubbing brush until completely clean.
2. Rinse with water and dry it completely.
3. Soak a clean cloth with white vinegar. Rub the vinegar over the galvanized metal to remove any remaining dirt and to shine the galvanized metal.
4. Buff the galvanized metal with a plastic scrubbing pad to help shine the metal
5. Apply metal polish to the galvanized metal. Rub it into the metal with a soft cloth.
6. Buff the metal polish off with a clean cloth.
The only step which they didn't address in this film was how to protect the now-cleaned surface from further oxidation. A light wax or oil? Lemon Pledge? or ??