How do you turn on the controller of an e-bike without a display?

The display is now a key component of any electric bike. But what should you do if it suddenly breaks down, gets stolen, or you simply can’t find it? Good news: in many cases, it’s entirely possible to activate your e-bike’s controller directly without using the display. In this article, I’ll explain how an e-bike’s electronic system works and how to manually activate the controller so you can get back on the road right away.

What is an e-bike controller, and what is it used for?

To understand how to start an e-bike without a display, you first need to know what the controller actually is. It’s often referred to as the “brain” or the “computer” of the e-bike. While the battery provides the power and the motor provides the physical propulsion, it’s the controller that manages communication and the flow of current between all these components.

In practical terms, it is a metal or plastic enclosure filled with electronic circuits, capacitors, and microprocessors. Its main functions are:

• Current control: It regulates the amount of electricity sent from the battery to the motor, based on your speed and the selected assistance mode.
• Signal processing: It receives and interprets data from various sensors, such as the pedal assist (PAS) sensor, the rotation sensor, the brake sensors, and the throttle, if the bike is equipped with them.
• Safety: It protects the battery from over-discharge and the motor from overheating or overload.

Without a properly functioning controller, the motor simply cannot run, even with a 100% charged battery. In fact, if you regularly experience issues with the motor’s assistance, our article on e-bike motor problems will help you distinguish between a motor malfunction and a controller malfunction.

The connection between the screen and the controller

Many cyclists think that the display is the bike's computer. This is a common misconception: the display is actually nothing more than the “user interface,” or the remote control for the controller. It shows information (speed, battery level, distance traveled) and sends your commands—such as changing the assist mode or turning on the lights—to the controller.

This connection is based on a specific communication protocol. When you press the on/off button on the display, it closes an electronic circuit. The controller then receives the signal to start up and supply power to the rest of the system. On most electric bikes, the main power supply passes through the controller before reaching the display. As soon as the display is disconnected, this circuit remains open: the controller no longer receives a startup signal and remains in standby mode, or even completely powered off. To turn on the controller without the display, you must therefore manually replicate this signal.

How do I turn on the controller without a screen?

To manually activate the controller, you must short-circuit the correct wires in the display cable. Caution: This procedure requires precision. An incorrect connection can cause a short circuit and permanently damage the controller or the battery. Always remove the battery from the bike before touching the wiring. Here are the steps to activate a standard controller.

Step 1: Locate the display cable

Follow the cable running down from the handlebar—where the display was attached—to the controller. The controller is usually hidden inside the frame, near the bottom bracket or in the battery mount. Locate the connector to which the display was connected: it is often a waterproof 4-, 5-, or 6-pin connector.

Step 2: Identify the colors of the wires

If you cut the connector or look at the wires on the back of the controller, you'll see several colors. On most universal e-bike systems, a standard color code is used: red for the battery’s positive terminal (V+), blue for the lock/power switch, black for ground (GND), and green and yellow (or white) for receiving and transmitting data (RX/TX).

Step 3: Bridge the wires

To signal the controller to start, connect the battery's positive terminal (red) directly to the ignition wire (blue). Use a small piece of copper wire or a paper clip to create a bridge between the red and blue pins on the connector. As soon as these two wires are connected, the circuit closes, just as if you had pressed the on/off button on the screen.

Step 4: Test and insulate the assembly

Reinsert the battery into the bike and turn it on. If you spin the pedals and the motor starts up, the activation was successful. The bike will then operate by default in a basic assist mode (often level 1, or the last mode saved). Immediately and properly insulate the bypass with electrical tape or heat-shrink tubing to prevent any contact between the bare wires and the frame or the black ground wire—which would cause a short circuit.

Important exception: closed systems (Bosch, Shimano, Bafang)

The method described above works very well on universal e-bikes and conversion kits. However, on high-end systems from brands like Bosch, Shimano, or certain closed-loop Bafang systems, it won’t work! These systems use encrypted digital communication (CAN bus or UART). Without a display, the controller won’t recognize the expected digital “handshake” and will refuse to start, even if you jumper the wires. If your bike displays an error message instead of a black screen, it’s best to first consult our guide to e-bike error codes or, for a Bosch model specifically, our article on Bosch error codes.

In many cases, a Bosch display that stays black isn't actually a controller malfunction, but simply an issue with the display or the internal battery. Before taking anything apart, check out our comprehensive guide on Bosch displays that aren't working, or—if you're riding a Purion model—our article specifically about Bosch Purion displays that won't turn on.

In a nutshell

Turning on the controller of an e-bike without a display is entirely possible in many cases, provided your bike uses a universal or analog-controlled system. By connecting the power wire (red) to the ignition wire (blue), you bypass the display and directly activate the bike’s control unit. You’ll certainly lose some features—such as viewing your speed or changing the assist mode—but this is an excellent workaround to keep riding. However, always proceed with caution to avoid damaging the electronics, and always opt to purchase an official replacement part for modern, digitally locked systems. A helpful reminder: a poorly maintained battery can also cause malfunctions that have nothing to do with the controller. So remember to reset your e-bike’s battery from time to time to extend its lifespan.

FAQ

Can you use an e-bike without a display?

Yes, on many universal e-bikes, this is possible by manually activating the controller. The bike will then generally operate in a fixed assist mode, but features such as the speed display, battery level indicator, or the ability to change the assist level will no longer be available.

Which wires do you need to connect to turn on the controller without a screen?

On most universal systems, you must connect the red power wire (V+) to the blue ignition wire (switch). Always perform this step carefully, with the battery removed, to prevent damage or a short circuit.

Does this method also work on Bosch, Shimano, or Bafang e-bikes?

No. The closed systems from Bosch, Shimano, and certain Bafang models use encrypted communication. Without the original display or an official solution from the manufacturer, the controller will not start up.

Written by: Dieter Devriendt | Published on: July 17, 2026 | 6-minute read

About the Author: Dieter Devriendt

A passionate journalist, Dieter writes about cycling with expertise and enthusiasm. Under the motto “we write—we ride,” he gladly shares his experience to help cyclists get the most out of their lives both on and off the bike.