The controller is a bit like an electronic ignition computer in a car. Its function is to convert the raw DC from the battery into a variable signal that activates the motor. For brushless motors, there are usually eight wires to the motor: 3 thick wires and five thin wires. Five thin wires tell the computer what\s happening to the motor. You can buy best Trek electric bikes parts and bikes also for better performance in Trek ebike. It then uses that information to send a timed pulse of energy through three large wires. Each wire receives a pulse just in time for the magnet to pass through the coil of the motor. Therefore, timings 123 and 123 make the magnet want to move to the next coil. The controller also limits the power supplied to the motor. In this way, the motor can operate at power levels that do not damage the battery, meet legal power limits, or simply limit power to make it more economical. You can test your brushless controller with the same brushless motor tester.