Ok, to test the wiper system you have to make sure that your meter's black lead is connected to battery negative at the battery terminal itself. This is the common reference ground point for all the electrical circuits. Any circuit voltage testing that you do the meter has to be connected to a known good ground or else you'll get inaccurate results. The only time you would want to use both leads to measure something in a circuit is if your doing a voltage drop measurement across a component, connector, or section of wiring, measuring amperage, or measuring continuity.
Next, you need to have the circuit operational to test it properly. With the connector unplugged all your seeing is open source voltage. If you have a resistance problem you won't see it measuring open source voltage because there is no current flow. You need to back probe the connector, with it plugged in and circuit turned on, at each circuit with your meter's red lead.
Write down the voltages you see on each of those wires.