WarIsOver wrote: ↑
Feb 13 2018 3:57pm
...how can it be that the yellow wire hasn't gotten any damage?
If you examine the damage closely, you will see that the heating is not in the wire proper (no melted insulation) and not in the bolted connection (no discoloration in the bolt or plastic insulator block), it's in the crimp. The discoloration in the ring terminal starts at the terminal crimp where things are melted and fades away towards the bolt.
For some reason that we can't see because the heat shrink didn't melt, the yellow wire had an effective crimp whereas the other two did not. Looking at the visible crimps in the two melted wire runs, there is really no useful crimp - the sleeve is just folded into place over the wire and really is pretty ineffective.
The crimp should be broad and completely crush the ring terminal sleeve with the wires inside into a solid block of copper with a gas-tight seal. You need a much better crimper (ratcheting, etc). Use the more expensive thicker copper terminals as well - not the cheap thin junk.
There is nothing wrong with bolted connections - they were the standard in the automotive industry for the better part of a century and are still used where high currents are present. They are essentially impervious to vibration and make an excellent electrical connection as long as the underlying bolt has a shoulder against which the ring terminal is tightened or the housing is bakelite (hi-temp and doesn't flow under pressure to allow things to loosen). The only reason they are not prevalent in ebikes is because of the size and inconvenience. If you can afford the space, keep on using them, but get your connectors attached to the wire properly.