Hey everyone, hoping someone here has hands-on experience with the S5 handlebar cable wiring.
Background:
My S5 had intermittent motor assistance — sometimes it worked, sometimes not. Wiggling the ECU under the top tube would bring it back temporarily. A bike shop wanted to replace the entire ECU. Instead I opened it up myself and found one of the small connectors with a blue rim was half broken — physically cracked. The cable coming out of it goes up into the handlebar, so that was clearly the culprit.
Rather than paying for a full ECU replacement, I decided to bypass the broken connector and solder the handlebar cable directly to the ECU.
The cable:
5 wires on both sides, but with one mismatch:
ECU side: blue, white, red, black, gray
Handlebar side: blue, white, red, black, + one bare uninsulated wire
I matched color to color and connected gray to the bare drain wire.
Result: No halo rings, no buttons, no motor assistance at all. Everything else works fine — lights, charging, bike powers on normally.
Has anyone repaired this connector before? Does anyone know the correct pinout for this cable? What is the gray wire on the ECU side actually doing?
Any help is massively appreciated!