Maybe it was wrong in this context. Could you give us a bit more text or was it a headline?

Stream of conscious (without ness) is a writing style. Maybe this was the mistake, but I can't tell anything for sure without quotes, sources or context.

normally you would only hyphenate these types of words if you are using them as an adjective/descriptor

in his stream-of-consciousness state (might be a lousy example, but you get the picture :))

ps - stream of consciousness (I have never heard "conscious" used like this); yes, it is on google... but that doesn't mean it's right

The term is a technique mostly used in modern novels. One example could be this quote by Humphrey that "the stream of consciousness novel is identified most quickly by its subject matter".
In this example it is written without hyphens....

agree about hyphens in adjectival use

OT: one of the best scenes in the “Third Man” is Holly Martens being flummoxed by a question about the “stream of consciousness” – I trust even some of the younger Leonites will have heard of the movie ;-)

I agree with #2 re stream of conscious - this can't be right as conscious is not a noun.

As for hyphens or no hyphens: I would write "the stream of consciousness novel" (#3) with hyphens, hence the stream-of-consciousness novel as it is used adjectivally (as #2 also points out). Having said that, English is far less prescriptive about these things than German.

Thank you for your help, but after reading through some more books in which the stream of consciousness is explained I find both spellings regardless of them being used as an adjective or noun.
This is just frustrating. Maybe it depends on the time? In older books the hyphen is more preferred than in more recent books.

[i]In older books the hyphen is more preferred than in more recent books.

unfortunately, that's not surprising; you'll probably find recent examples where hyphens have not been used although the phrase is used adjectivally

I guess I get it now and know how to use the hyphens correctly.

Thanks!