Siemens Se25M570GB/17 Circulation Motor Issues

Hello,
I’m hoping for some advice on the above model dishwasher, which we’ve had for many years. I’ve kept it running over this time, and had to replace some solenoid valves, and the heat exchanger.
However, after returning from holidays I found that the circulation motor had seized up completely. I removed the motor, and it has indeed completely seized solid, and I could not even turn the shaft. So I ordered up a replacement (second-hand, but told was tested and working).
Reinstalled this, and for the first 30seconds or so, all was well with the machine, but then there was a burning smell and some smoke from the motor. I immediately thrned the machine off, and rechecked all connections etc. All were good, and I measured the capacitor with my fluke and it tested fine. Tried again – same issue, but this time I lost the control board also. I then believed there was a board issue which was causing a knock-on motor problem.
Managed to get a replacement board, at some cost, and just reinstalled it. Same issue again with the motor, in that after it runs, there will be a burning/smoke appearance. I was waiting for it to hapen this time about, so I had it disconnected pretty much immediately as I feared losing yet another board.
I have narrowed the issue down to terminal 4 (pink wire) on the motor. If this is disconnected the motor will run fine throughout the cycle, and no burning/smoke.
Therefore, whatever aspect of the motor this controls, the motor is having issue with. I doubt there is now q control board fault, as the board came direct from Siemens.
I attach a pic of the connections, and would be grateful if anybody has an opinion. What I’m really trying to ascertain is what exactly the pink feed does for the motor – is it a speed, torque or reverse function? Can I leave it dosconnected, at the least until I can source another replacement motor? Any ideas, motor operational explanation greatly received.
Thanks in advance.
Regards
Ger