Alright, so it sounds like your brakes, motor, battery, and switch are all good. So that pretty much leaves the throttle and the controller.
A little caveat about my advice about testing throttles and controllers, I've never actually tested these before with a multimeter, as I ended up getting a Lyen tester ( viewtopic.php?f=31&t=20413
) before I got to this point on my repairs. Perhaps someone else can lend some more experienced advice.
Ampedbikes has had a few different types of throttles. Mine is a big white plug, similar looking to the hall sensor plug that goes from the motor to controller. The throttle itself is a hall effect sensor setup, similar the motor. Except there are 4 wires instead of 5. So you should be able to test it in the same way you tested the motor before. Set the multimeter to measure volts, and test between red and black, that should register about 5 volts. My throttle's other two wires are yellow and green. So if it's the same, you test from yellow to black, and then green to black. The voltage should vary between 0v and 5v depending on how far you pull the throttle down.
If the throttle appears to be fine, then that pretty much leaves the controller. I don't have much advice on how to test that...