Reddit mentions of Harrier in Action - Aircraft No. 58

Try the flight sim crowd; a lot of them build custom aircraft, and as a result, they have references.

See e.g.

http://www.razbamsims.com/downloads/Docs/RAZBAM%20Harrier%20GR.7-GR.9%20Aircraft%20Manual.pdf

GR7/9 manual for a flights sim, which includes renderings of some of the cockpit parts. Not quite on point, but you see what I mean.

See also:

http://publicintelligence.net/u-s-navy-natops-av-8b-harrier-ii-flight-manuals/

This is a flight manual which I haven't perused in some time, but perhaps there is something in there with a master reference to the master caution lights, panels, etc.

If nothing else, perhaps it's interesting reading.

Your best bet will be either the flights sim crowd, or a google search for various images; a comprehensive resource out there might also exist among british modelmakers sites.

British modelers seem to have these things called "SIGs" (Special Interest Groups) that may or may not be offshoots of IPMS chapters, but devoted to a very particular subject or aircraft. In that case, see if there is one for harriers; they are the people most likely to have accumulated reference materials. Try also military archives of the relevant nation state you're looking for references for; it's a long shot but sometimes you can find interesting or useful stuff.

Never mind, they exist:

http://www.harriersig.org.uk/

See also:

Harrier GR3 specific references:
http://p1127.co.uk/Harrier/index.html

List of recommended references for modelling Harriers generally:
http://www.harriersig.org.uk/models/modellingtheharrierv3.pdf

Osprey Publishing references, and a sample on google books.
http://books.google.com/books?id=HRTW6VXy780C&pg=PA71&lpg=PA71&dq=special+interest+group+harrier+modelers&source=bl&ots=u8KPzrHNYO&sig=hMJk1fXzZfVTabNdkSpN9-vZVkk&hl=en&sa=X&ei=sSBYVOSiCIHmsAS554CIAQ&ved=0CDIQ6AEwAw#v=onepage&q=special%20interest%20group%20harrier%20modelers&f=false

Finally, you can look at 3d modelers forums (e.g. the types that make digital models for flight sims, games, and just for the hell of it). A lot of them will gather up references for the particular aircraft they are modelling, or have/seek threads that ask for such materials.


And finally, because I can be an insufferable know it all, Squadron and Osprey might publish stuff with some references, but they are not definitive. Sometimes they will showcase subtle differences among marks and variants, but I can't vouch for the quality of this:

http://www.amazon.com/Harrier-Action-Aircraft-No-58/dp/0897471393/ref=sr_1_1?ie=UTF8&qid=1415062102&sr=8-1&keywords=harrier+in+action

See finally:

http://www.kitsforcash.com/harrier-gr3-cockpit-detailing-set-21-p.asp

Resin cockpit set designed specifically for the model in question. Perhaps you might consider that instead of scratchbuilding, but perhaps you want the challenge.