The official NASA history of the Saturn vehicles "Stages to Saturn", pp. 361-362 agrees that there was a miswired control cable.
..the low-thrust sensing equipment triggered a sequence to shut down
the engine by closing the fuel and oxidizer valves. The electrical
sequence to close number two LOX valve went erroneously to number
three. Closing the fuel valve for engine number two and the oxygen
valve for engine number three shut down both engines.
(The second occurrence of "sequence" appears to be an error; it should probably read "signal".)
I have the print version of the book, but in the online one it's on this page (look for the ).
This chapter also discusses the ground investigation via the telemetry data in some detail. The root cause was a rupture of the igniter propellant lines due to resonant vibration. Ground testing had not identified the failure mode because when the engines were fired in an atmosphere, air that liquefied on the lines dampened the oscillation enough to prevent failure.
There is an extremely detailed analysis of the failure in this document, which I just noticed in the excellent answer to this question: How common is the ability to compensate for a lost engine through gimbaling?