This 1995 Chevrolet Monte Carlo came in with the complain that the brake / stop lights do not work. As long as all of the bulbs are working this is easy to test. First confirm that the stop lights in fact do not work. Then check the turn signals and hazard lights. If they work the bulbs and wiring from the turn signal switch are okay. Have some one depress the brake pedal and check to see if the third or CHMSL is working. If it is and the lower ones are not the turn signal switch is faulty. If it is not either check the bulbs for that light (accessed through the trunk) or drop the lower dash cover and test the wiring. I checked and changed the CHMSL bulbs and that light started working so diagnosis of faulty turn signal switch.
I removed the screws from the lower dash cover and removed the cover.
I also removed the steel cover that is under the plastic panel.
I checked for power on the light blue wire (input from stoplight switch) with the brake pedal depressed. Power, this again confirms that the fuse and the stoplight switch are both good.
I checked the green and yellow wires (turn signal and brake light signal to the rear of the car) with the brake pedal depressed and the turn signal switch in the neutral position. No power and again I have diagnosed a faulty turn signal switch. By the way on many vehicle the turn signal switch is referred to as a multifunction switch.
To see how to replace the switch please click here.