Make sure your bike it turned off. Remove the battery and discharge excess electricity by powering on the display with the battery removed.
Use a Philips screwdriver to remove these 3 screws and remove the motor cover.
Snip the zip ties connecting the speed sensor wire to the lower chain stay.
Undo this bolt with a 4mm Allen Key. Make note of any bolts or spacers inbetween the speed sensor and the frame - make sure to install these correctly with your new speed sensor
Trace the speed sensor wire into the area you opened up in Step 2 which will be referred to as the wiring cavity. Find the connector - the circled one in the picture below. You will need to pull out some other wires to access this - take care while doing this. Squeeze the sides of the connector and unplug it.
Pull the old speed sensor wire out from the wiring cavity and fully remove the old speed sensor from the bike
Insert the connector for the new speed sensor into the motor wiring cavity through the hole you pulled the old one out from. Plug the connector into the plug on the motor where you unplugged the old speed sensor from.
Screw the new speed sensor into the hole on the rear chain stay where the old speed sensor was attached. Ensure that you have correctly reinstalled any spacing bolts! Take care to not cross thread this bolt while screwing it in - you may need to start it by hand before using a tool to further tighten it. Make sure it is aligned and oriented correctly - see this image below for reference.
Zip tie the wire from the new speed sensor back onto the frame. Push the wires you pulled out back into the wiring cavity and screw the motor cover back on.
Check that your newly installed speed sensor is working correctly and your issue is resolved.
If you are still having trouble, please submit a support ticket using the same email you placed your order under. Please note in the ticket your Biktrix order number, the trouble you are experiencing and include photos of the issue.