The microswitch in the door lock unit had been worn out.

I bought a new lock unit on ebay.

I let a wellknown garage (but not Skoda authorized)  switch the locks.

Now the red LED lamp on the drivers door does't start to flash.

When they had the door open they also disconnected the connector to the door control unit to check if the pins were erroded.

Can it have something to do with that? Is there a reset to be done maybe?

I shall go back to the garage but I thought I could ask the question here to see if anybody recognize this error.

Maybe it's so simple that they have forget to reconnect the 2-pin connector to the lamp.

Take it back to the garage. Could be many of your suggestions, but if you paid someone to do it they should sort it at no charge 

Post removed in edit.

Edited 16 July, 20178 yr by pikpilot