Personnel in wheeled vehicles should take what action before vehicle wash down?

Turn off the engine of the car and close the car windows.

Explanation:

Before going into the car wash, personnel still sitting in the car must turn off the engine of the car so that nothing unfortunate may occur. The most important action that must be taken is the closing of windows.

If the windows are kept open, the person sitting will also get a wash alongside. All the soap and water will rush into the car and it can very quickly turn into a miserable experience.