MB Stars you are excellent. That's exactly what happened. I turned back the ignition key a little bit and the fan was then started.
So, you are right at the dot that I would need to replace the ignition switch behind the steering lock assembly.
Please also enlighten on what other possible problems a faulty steering lock assembly could cause in future, which you mentioned in your post earlier. Thanks.
W123, 1984, 2Litre gasoline, manual