Working knowledge of automobiles and engines in particular certainly helps but is not absolutely necessary IMHO. I have never assembled a 1:1 engine but have built some fairly accurate scale replicas. Thankfully in model car world things only need to look the part.
There is a wealth of information now on the internet on just about any car you would care to build. Some things I find useful:
plumbing and wiring diagrams
restoration photos and videos
automotive parts websites
car related forums
And when I really get stuck I turn to help form this forum, no shame in asking a question.