How to connect a windshield wiper motor to a DC power supply
It's funny that you bring this topic up because I just dealt with this whole scenario about a week ago when I was diagnosing my niece's windshield wiper motor.

Any modern car is going to have five connections on the motor. One is a ground. There are two wires for positive, one for low speed of the wiper motor and another for high speed. Then, there are two more wires that are used like a switch to determine when the windshield wiper is in "home" position. 

But you only have four connections you say? Well, this tells me that the case itself is the ground and that the other four terminals correspond to the other four connections mentioned.

I would measure the resistance between each pin and the case (ground). There should be two pins that measure infinite resistance because they are not connected to ground in any way. These are the two wires that determine when the windshield wiper motor is at the home position.

The other two wires are the high speed and low speed wires. Take your pick and try one and see which one is faster.

Edit: After further looking, it seems that one of the pins IS the ground. This means it doesn't have two speeds or that the home position switch is only one wire.