As I mentioned earlier, if you connect the test leads backward, you'll just get a minus sign in front of the numbers. Ignore that and just read the numbers.
One meter lead goes to ground, which is the car's metal body. Look for a rust and paint-free point such as a bolt head. I use a clip lead so I don't have to hold that probe all the time. You won't be taking enough readings to warrant investing the three bucks in a set of clip leads. Use the black lead, which is plugged into the meter's lowest "common" or "negative" jack. That is the standard connection and will insure you won't see the negative sign.
As an important comment of value, I spent a good two or three minutes showing my students how to verify that ground probe was making good contact. If it doesn't bite through a light film of corrosion, you'll get all readings of 0.00 volts. That COULD be the result of there really is 0.00 volts there, but if there's 12 volts, and the meter only sees 0.00 volts, you just made the wrong decision and went down the wrong diagnostic path. As the professional I claim to be, I've done that very often. For this discussion, if you find 12.0 volts on any terminal, the ground connection has to be good, so we can move on.
Whichever rear switch you're on, you have a dark blue wire and a brown wire. Probe either one with the red meter lead. Activate the switch one way, then the other way. Move the probe to the other wire and do the same thing. What you SHOULD see is only one of those wires becomes 12 volts when you push the switch one way, AND only the other wire has 12 volts when you push the switch the other way.
Given the symptom, you're going to either find 12 volts on BOTH wires when the switch is pressed either way, or you're going to continue to see 0.00 volts when the switch is pressed. Once you've made the observations, you are welcome to complicate the story by watching what you get when a helper presses the driver's switch either way.
I'll be out of town for the weekend at an old car show swap meet. I'll be back Monday night to see how you're doing.
Wednesday, April 26th, 2017 AT 3:31 PM