They are fusing together because of too much heat build up, is it the wire covering melting or the connector ?
The heat shrink as you now have used is the answer.
The fault was as I suspected yesterday when I replied to your thread, a phase /controller issue. The loud cracking noise you heard was electric static of the phase wires shorting, many a person assumes it is the motor grinding but confuse the two sounds.
The reason for melting is either , too much current is being used esp at low speed or the wiring is too thin and can't handle the current being drawn.
In your case a combo of the two, it is clear in the pic that one set of phases are alot thicker then the others they connect to so there is a bottle neck of current that gets very hot at the connector. This clearly has led to excess heat and melting /fusing of the wires.
If the thinner wires are from the controller thenit makes sense to open the controller and replace the thin wires with thicker awg silicone wires to the joint.
If the thinner wires are the motor side then not much one can do except to reduce the current. If the controller uses current control then use less current via a lower PAS level when riding slow or slowly up hills.
Thanks for your reply Nealh.
I put those heat shrink coverings on a couple of years ago. This morning, when I opened the controller, nothing looked damaged; they were just slightly stuck together, so I separated them (as in the pic) and switched on the throttle and it worked straight away.
In response to your question, i think the issue is from the motor end wires. I think the contacts are not great, as I've had to tighten them and put seals on them to prevent fusing as before.
I had the bike in gear 2 when I attempted to start off, but I will go down to 1 to start off in future. The PAS is current with 6 Shimano gears. Cadence sensor too.
I'll get some high insulation tape as Andy suggested and hope that keeps them separate.
Thanks again