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Jim Grant's Tech Tips
`92 Mercury Sable, Who Broke My Car?
Q:
Prior to a trip I was going to make, I took my ’92 Mercury Sable into the garage for a complete going over-belts, fluids, etc.. The car was put on a lift & two men worked under it. Then after lowering it, went in from the top under the hood. The car was functioning beautifully and still does except that the next day, I could not raise the back windows up after I’d lowered them (using the driver’s armrest button). They disavowed any responsibility and never offered to locate the problem. If you went to the back door and pressed the button to raise the window, it did close. It was only because of a 300 mile trip each way that I even brought it in for this extensive exam at a cost of $300-$400 at that time. It’s always properly serviced as needed. Have you any suggestions as to why the driver could lower the rear windows but not raise them? Yet, when done directly on the back door’s armrest, they work?
A:
That is simple, you have a bad master switch. The master switch is the power window switch at the driver’s door. How do we know this? The fact that the rear power window works with the rear switches proves that the power window motor, switch at the door and wiring to that power window is good. The electrical power for those rear windows has to go through the master power window switch. Power windows are wired somewhat like lights in a house that you can turn on or off at 2 different places. The electrical power travels through both switches and wiring to get to the light. In your case it is not a light, it is an electric motor and one of the switches is not working in one direction. The master power switch fails most often due to corrosion followed closely by wear. No one will argue that the driver’s side door is the most used door of the vehicle. The driver’s side door is one of the worst possible locations for an electrical switch. Whenever it is raining or snowing and the driver’s door is opened the master switch gets wet. Open the driver’s window in the same weather conditions guess what gets dripped on? To make matters worse the master switch is recessed so dirt and debris collect and work their way down into the switch. Over time those drops of water and debris add up and the switch fails. Your vehicle is 14 model years old, stuff like this happens. I’ve installed a lot of master switches on vehicles much newer than yours for the same reason. The bottom line, the shop that serviced your vehicle is not responsible for your master switch failing, it happens. You should not expect them to diagnose or repair the problem free of charge just because they serviced your car. In the trade we call that the “ever since you touched it” syndrome.
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