How do u install an external speed sensor on a carrera subway ebike

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I’ve got this bike from a friend cos he was relocating but bike has an error 21 I ordered an external sped sensor on Amazon but do not understand the wiring. Need help

 

[saneagle]

I’ve got this bike from a friend cos he was relocating but bike has an error 21 I ordered an external sped sensor on Amazon but do not understand the wiring. Need help

Red wire goes to any 5v. black wire goes to any ground and the other wire goes to the speed sensor signal wire on the controller. TI can't remember if any Subways had the Bafang motor and standard Chines stuff. I don't think they did, but you need to say if that's what you have instead of the Suntour HESC system. Whichever system you have, it's not easy to get at the speed signal wire that's in the motor cable (probably white). I think you have to hack into it, then you can cut it and splice yours on and splice into the 5v and ground wires there too, but don't cut them.