How do you tell if it is the motor or regulator that is causing a window to go down but not up on a 2000 Toyota Sienna?

Disconnect the power window switch plug from the connector that connects it to the motor inside the door. It should be like a male and female type plug, all you need to di is locate the tab and slide the 2 apart. The circuit that remains on the door will be the one that goes down to the motor inside the door. The plug you want is the one under the switch that you push back and forth for up and down. Get a circuit tester small handheld unti that reads voltage and ohms and etc. (usually for less then $20.00). Make sure your circuit tester has a good battery. Turn the meter on and set it to DC volts and set it to 20. You are looking for a reading roughly to be 12volts on the meter. You will see the circuit tester has a red and black wire. Look at the connector and insert the lead of the red end into either the up or down terminal. Put the Black wire to a ground. Turn your ignition on, the meter should read zero. If you have the red lead against or in the up terminal, push the power window switch like you want to raise the window and watch the meter. You should get voltage, maybe 12 volts to read on the meter. The switch should allow the voltage to go to the motor to run the window mechanism to raise your window. Now try it but put the red lead on the DOWN side of the switch with the Black lead still connected to a ground. See if you get a reading on that. If your swicth is only working on one side I would suspect a faulty window switch. BUT if you get a voltage reading on the meter on both the up and down side tests, then this shows the voltage i s getting through the switch and now your problem lies in the window motor itself. The window switch should, note should be cheaper to replace than the motor but in today's electronics, who knows. If you have never used a circuit tester before, read the manual so you will know how to use it.