I found a method how to add an autocomplete function to a simple textbox by using the following code:
What I did:
I created 2 list. List "A" have a text column to support the autocomplete function. List "B" have a simple textfield what should be autocomplete when the user start to write.
I went to the input display of the "B" target list (New item).
I added script editor web part from "Media and content".
I copyed the script from the link.
Modyfied the names of the lists.
Result: When I save the script editor I can see an error message for a sec: "AsyncDeltaManager.ParseErrorExeption: The messege recived from the server could not be parsed". And nothing happens. I am new to both Jquery and Sharepoint so it can be even a trivial mistake. Also the guide was for SP 2010 and I am using 2013.
Thank you very much for any suggestion!