A bad motor will keep on running as long as it is on. It will fail to start up when you hop in the van and start it. If it stopped running while you were driving, it is more likely due to a defective resistor assembly or switch.
The best place to start is by checking for voltage on the connector for the motor. It's just above where the front passenger's right foot would be. Use a test light or voltmeter to measure the voltage on the two wires. The black wire should have 0 volts and the voltage on the green wire will vary depending on the speed selected. If you find 0 volts on the green wire, head to the switch next. If you have the center console that goes down to the floor, you'll have to unbolt that to get to the two lower screws for the trim plate around the radio. Remove the switch and measure the voltages on the wires. One of them must have 12 volts. Remember, the ignition switch must be turned on when making these measurements.