The Audi A61.8T car with a mileage of over 350 thousand km in 2000. User response: the vehicle occasionally fails after the ignition switch is closed. Inspection and analysis: the first doubt that the vehicle can not be extinguished is that the No. 15 power supply on the ignition switch has no normal power break, so the ignition switch is removed and the line 15 is measured with a multimeter. Sure enough, there will be 12V voltage occasionally after the ignition switch is closed, that is to say, line 15 is short circuited with line 30. Because the vehicle harness is very well tied up, the inspection of the ignition switch and the wire harness is not simple. In order to avoid destructive maintenance, it is determined that the 15 power supply and the No. 30 power supply on the ignition switch are not short circuited. The maintenance is in the deadlock for the time being. At this time, the user talked about a phenomenon: if a fault occurs, if the pedal is pressed, the vehicle will stall. So the maintenance staff found the relevant circuit diagram analysis, found that the brake lamp switch 4 foot is connected to the No. 30 power supply, 2 foot is connected to the 15 power supply, if the 2 feet short circuit will cause the vehicle can not be flameout. Remove the brake light switch, use the hand repeatedly to operate the push rod, and use the multimeter to measure the break between the 2 and the 4 feet, and it is found that at some time 2, 4 feet are through. Shake the brake light switch and you can hear the noise inside. Disintegrate the brake light switch and find that one end of the reed is broken, so that the reed is sometimes stuck between 2 and 4 feet, making the 15 line and 30 ordinary fire line through, so that the failure of the car appears. Troubleshooting: replace brake light switch and troubleshooting.