A recent post to the Fender Forums (see: contains several links to PDF's purportedly of the Fender Mustang Schematics.

Hi all, This is my first post in Fender Forums.  I'm a 5 year owner of a Strato American Deluxe HSS, and I just purchased a Mustang IV (V.2).
In the urge of finding out the most about this awesome amplifier I came across a lot of users wanting to access the schematics of their amplifiers. Having an Electrical Engineering degree and being curious as hell, I began searching those around, and after doing some advanced Google searching I stumbled upon these:
Mustang V
Mustang IV
Mustang III
Mustang I & II
Mustang Mini
Mustang Floor
They appear to be legit, but of course I can't tell it for sure.
Disclaimer: I'm not responsible for these files neither I have control over their availability. They are publicly available through a Google link resulting from a trivial search string.