You got me now. The only reason I know about the switch is a former student calls me to chat a couple of times per week and he likes to share some of his stories. He had a GM car last week with the dead main brake lights and just the high-mount one working. On older cars, after leaving the switch, one wire goes to the high-mount light and one goes to the turn signal switch, then to the two brake lights. That is on cars where the brake light and turn signal light are one and the same. His problem was caused by the brake light switch.
The cruise control is tied in, typically on both sides of the main brake light switch which is normally closed, but held open when the pedal pushes it back. When it closes, voltage is sent to the signal switch and to the Engine Computer or cruise control module for the "cancel" signal. Something in the system, commonly the servo, gets its voltage from the feed side of the brake light switch. That is so the cruise control won't work if the brake light fuse is blown. If that fuse is blown, there would be no way to get that cancel signal when you tap the pedal, and the car would keep on going until they found you in the next county!
Some Chrysler models use a third switch inside the brake light switch for the cruise control system. That one is normally open but is held closed when the pedal is released. Current flows through it to power the solenoids in the servo. That is like a backup to insure it cuts out when the brake pedal is tapped. Pitted contacts can prevent that system from working although that isn't real common. To set the system, the brake light circuit still has to be working, but as I recall, the cruise will still work if the brake light switch contacts are open.
I can't remember what I was told last week but the cruise control did provide the clue. I would assume it either didn't set at all or it didn't cancel when tapping the pedal. I find it hard to believe it would work and not cancel. Designing the system that way could leave them open to lawsuits. People will notice a non-working cruise control and investigate further, but most drivers will not notice non-working brake lights.
First look at how many wires go to the switch. On the off chance there's only two, that switch has to be good if the high-mount light is working. Then suspect the turn signal, (multifunction), switch. If your rear signal light bulbs are different than the brake lights, all three brake lights should be wired together. In that case, look for a corroded splice, cut wire, or rusted ground wire. Your car is too new to be expecting corrosion already. What I would expect to find would be where someone used a ScotchLok connector to splice in a wire for a trailer harness. Those connectors don't seal out moisture.
If your brake light switch has four or six wires, you're going to just have to check with the voltmeter to see if voltage switches state when you press the pedal. On older cars, the orange wire was the 12 volt feed and the white wire was the switched 12 volts that went to the signal switch.
Tuesday, January 17th, 2012 AT 4:50 PM