I just want to ask: How true is this myth that I should never roll down my window after I get a car wash because the water may damage the wirings?
I can't say that it’s absolutely false, because there is a chance that water can get into the wiring if you do open your window immediately after a car wash. However, automotive wiring is meant to get wet. Cars are designed to get wet. Cars need to take you through, and protect you from weather that includes rainstorms.
The wiring they put into your car is designed and is supposed to be able to tolerate and resist water. These wires are insulated with water-resistant connectors and coated with dielectric grease that repels moisture. To a certain extent, automotive wiring has been designed to be, and is, water resistant.
However, I also can't say that having your car washed and getting your wiring wet is alright. A few drops are fine, but forcing pressurized water into connectors and boards isn't such a good idea. As a matter of fact, Jay Leno, one of the world’s most renowned car enthusiasts, advises to wash your car as little as possible if you want to preserve it. The fact of the matter is that water and humidity cause rust, and rust degrades metal and impedes electrical connections. So if you want to preserve your car, then you'll want to keep it in a dry space and wash it as sparingly as possible.
But then again, this is a car. Aside from the interest of preserving it, it is principally a tool that you use to get yourself to and from places comfortably--especially during wet weather. Also, as you use your car, it will unavoidably get dirty and will need to be cleaned and washed. Therefore, we must have a healthy balance between use and preservation.
I think we should draw the line at abuse. And to my mind, rolling down your window after a carwash isn't abusive at all. After all, the wires for your power windows, locks, and mirrors are on the inner side of the window, and what gets wet is the outer side. After having your car washed and opening your window, only a few drops of water will probably get into the inner side of the window, and possibly less onto your wiring. I think the water resistance designed and built into the car's wiring will be able to withstand that much.
In closing, I've seen cars that are over 20 years old and the wiring in their doors are fine. Sometimes, the window regulators, motors, and wiring have to be repaired or replaced. But if you’re a conscientious owner, these things can be fixed, and are all just a part of car ownership. Don’t worry too much about preservation unless your car is a valued collectible and you want to keep it in pristine condition for all time.
Hope this answers your query. Thanks for writing in!