Well, there's your answer then, the voltage isn't making it to the pump motor. I would first try to put the red lead from the meter on the power wire to the pump and then take the black meter lead to a known good ground like the engine block. If voltage is still low, it has something to do with the power wire itself. If you have good voltage, then test with the black meter lead to the other wire in the connector and if no good voltage then it is the ground wire.
Next, you'll need to see the source voltage at the fuse block. Go up under your dash down by the e-brake and you will find a fuse for the washer pump and wipers. Simply test the back of the fuse on the openings to see if there is power. If no power there, then it gets a bit more tricky, because then its time for digging through that wad of wires going into the fuse block. I highly doubt that is it though. I bet you have some corrosion on a ground somewhere, or a poor connection.
Good luck!