I have a 72 with the original wiper motor in there. When it is switched on, the little box that is clamped to the side of the motor clicks, but nothing happens. So, I bought a used motor and it does the exact same thing. Does anyone know where to begin troubleshooting? What exactly is that little box?

That clicking sound is likely a wiper motor relay and it's not getting suficient voltage....probably due to a poor ground or a corroded connector. This happens in old cars. Get yourself a service manual, ohm meter, and a power probe (awl like devise with a light in the handle and a lead coming off the handle with an alligator clip). It's just basic electrical circuit troubleshooting!

Thanks 240zx, I actually took it apart and saw the switches inside, all rusted. The motor is almost all rust inside too, save for the shaft. I guess it's time for a "new" motor. Does anyone know where to find one? I don't think I saw one in motorsport for the 240.