All of our controllers are tested to verify that they work so if a vehicle does not run after installing a new controller then the issue is usually with another part of the vehicle and not with the controller.
Here are some troubleshooting steps that we recommend when a vehicle does not run after installing a new controller:
1. Have a look at the controller's wiring directions page to make sure that all of the required connections are made to the controller. For most controllers, we have a copy of the wiring directions on the page that the controller is listed on.
2. Test for Voltage at the controller's battery connector to make sure that it is getting power from the battery or battery pack. If it is not getting power then there may be a bad wire, connector, blown fuse, or on some models a faulty switch that is causing the battery power to not reach the controller.
3. If a brake switch is connected to the controller then disconnect it to see if that helps. Sometimes brake switches will fail and lock into the on position which tells the controller to not run the motor.
4. Test the key or power switch for continuity when it is on to make sure that it works.
5. Test the throttle to make sure that it works. We have a Throttle Testing Guide page.
6. Test the motor by wiring it directly to a battery to make sure that it works (for brushed motors only).
7. Test the Voltage of the battery pack to make sure that it is at a 100% state of charge and if it is not then recharge the battery to bring it to a 100% state of charge. We have State of Charge Charts for lead-acid batteries and battery packs.
8. Test the battery Voltage with the power or key switch off to see if it is higher than the controller's low Voltage cutoff level. Then turn the power or key switch on and engage the throttle to the full throttle position while watching the battery pack Voltage to see if it drops under the controller's low Voltage cutoff level. If during this test the Voltage drops under the controller's low Voltage level that points toward an issue with the battery or battery pack.
9. Create a Support Ticket and send us a photo or photos showing all of the connections to the controller because we can sometimes help solve this type of issue by finding a miswiring that can be corrected.
We have a troubleshooting guide with more diagnostic steps on this page: https://www.electricscooterparts.com/troubleshootingspeedcontrollerdoesnotwork.html