Help - PWM DC Motor Speed Controller

Hopefully someone knows the answer to this. So I've got a monster guts wiper motor - works great when hooked directly to the power supply. I bought and connected a PWM DC Motor Speed Controller - checked to make sure the polarity is correct - seems obvious that it is connected AFTER the power converter - so it's DC to DC. When I plug it in - nothing - the wiper motor doesn't run.
Any ideas? I can't figure out what I could be doing wrong.