If your e-bike left the factory with a Bafang system that uses a separate controller, that controller is a box with a bundle of plugs. Replacing it, or tracing a fault, means knowing which plug is which and how they go back together. This guide walks through one documented example, the CR S307.1000.FC, using the interface table and cabling steps in Bafang's dealer manual (BF-DM-C-CR S307-EN, April 2022).
Scope: the manual covers a factory (OEM) controller (48V, 1000W rated input, CAN communication with the battery). It does not cover the separate controller box that ships with many aftermarket Bafang conversion kits, and we could not find that controller's wiring in Bafang's published dealer manuals. Kit owners should follow the paper manual in the box.
Rule zero: battery off
Switch the battery off and, where you can, remove it, then wait about 30 seconds before touching any connector. Plugging or unplugging the motor's phase wires with power on can spark and damage the controller's output transistors (MOSFETs). Photograph each connector before you separate it.
The six connections on the CR S307
The manual's interface table lists six connections:
| Connection | Pins | What it carries |
|---|---|---|
| Power | 2 | Red power +, black ground. |
| Motor | 11 | Phases, Hall sensors and a speed signal (details below). |
| Battery communication | 4 | CAN L, 5V, CAN H and one unused pin: a data link to the battery management system (BMS). |
| Torque sensor | 6 | 5V, ground, CAN L, CAN H and two signals. |
| Light cable | 2 × 2 | Two leads, each 6V/12V and ground; the manual lists headlight and taillight support (6V 3W or 12V 6W) without saying which lead is which. |
| EB-BUS | 8 | The handlebar cable (details below). |
The motor plug: 11 pins, and the colors repeat
Many hub motors use a 9-pin motor plug, but the CR S307's motor connection has 11 pins. The manual lists: 1 blue, phase A; 2 yellow, phase C; 3 green, phase B; 4 green, Hall H2; 5 white, speed signal; 6 yellow, Hall H3; 7 blue, Hall H1; 8 purple and 9 grey, both unused; 10 black, ground; 11 red, power +.
Blue, yellow and green each appear twice, once for a phase wire and once for a Hall signal, and the phase letters do not run A, B, C in pin order. Match by pin number, never by color alone. See our phase and Hall wiring guide.
Same color, different job
Colors also change meaning from plug to plug. White is the speed signal on the motor plug, CAN L on the torque sensor plug and the brake signal on the EB-BUS. Yellow is phase C on the motor plug but CAN L on the battery communication plug and on the EB-BUS. Red is power + on the power and motor plugs, but 5V on the battery communication and EB-BUS plugs.
Never wire by color across plugs, or assume another Bafang part uses the same scheme: even the 860C and 850C display manuals differ on three of five pin colors.
The EB-BUS: everything on the handlebar
The 8-pin EB-BUS carries the cockpit: throttle signal (blue), 5V (red), CAN L (yellow), brake signal (white), ground (black), key signal (orange), display power + (brown) and CAN H (green). A splitter harness such as Bafang's 1T4 branches an 8-pin EB-BUS trunk out to the display, throttle and both brake levers; see our main wiring harness guide. Because the brake signal travels on this cable, repeat the brake cutoff test after every reconnection; our brake sensor guide covers how that cutoff works.
The order to connect them
Section 10.3.1 of the manual numbers the cabling steps:
- Battery: the controller's communication cable (male) to the battery BMS cable (female), plus the power leads: controller negative (female) to battery negative (male), controller positive (male) to battery positive (female).
- Motor extension cable: female on the controller, male on the extension.
- EB-BUS: male on the controller, female on the EB-BUS cable.
- Speed sensor: female on the controller, male on the sensor.
- Light extension cable: female on the controller, male on the extension.
These steps do not map one-to-one onto the interface table: none covers the torque sensor plug, and the step 4 speed sensor has no table row. Never guess where an unlisted plug goes.
The sequence also varies by model. Bafang's dealer manual for a lower-power controller, the CR S10F.350.FC (rated 250/350W), lists battery, speed sensor, EB-BUS, motor, light and then display. Follow the manual for your exact controller and use its steps as a checklist. In the manual, "connect the battery" describes linking the cables; it does not mention switching the battery on. Keep the power off until the last plug is home, and never force a plug: check its pin count and alignment instead.
After the last plug
Switch the battery on and run a short check before riding, with the drive wheel lifted off the ground: the display powers up, the motor responds, and squeezing either brake lever cuts the motor immediately. Our post-install checklist covers each test. If anything is wrong, switch off again before you unplug anything.
Before ordering a replacement, read the model number on the controller's label and match it to that model's manual. Unsure what you have? Our guide to the four photos we need to confirm a part fits shows what to send.