I would like to add that the linked video deviates in major ways from the truth - or at least from the Greek accident board's assessment.
Firstly, the final report of the Air Accident Investigation & Aviation Safety Board (AAIASB) does not mention the wiring problems at all. Nor does it mention anyone noticing a "burning smell" as is said in the video. If they ever considered it a possibility it had obviously been ruled out before the final report was issued. In fact the report does reference several prior 737 pressurization incidents, each of which were attributed to failures in the operation of the controls and not any malfunction. Their recommendations all pertain to changes in the wording of procedures and changes in the cockpit warnings, i.e. a different warning horn and more noticeable indicators on the panel.
The firm conclusion of the investigation was that the pressurization switch had been left in the manual position and the pilots misinterpreted the warning horn. This was evidenced by
1) the position of the switch as it was found in the wreckage
The cabin pressure mode selector was confirmed to be in the MAN (manual) position by physical witness marks on the mode selector input shaft and by electrical continuity checks in the mode select circuitry. *
2) the Non-Volatile Memory (NVM) chip inside the controller
The NVM recording showed that on the accident flight, the cabin pressure control system was being operated in the manual mode. *
3) conversations with ground personnel
The Helios Dispatcher reported that the Captain referred to the Takeoff Configuration horn, and then the Equipment Cooling lights. *
The video also said that the the F-16 pilots saw two people struggling in the cockpit when they arrived. I have no idea where they got this (made it up maybe?) because the investigation states,
When the flight HCY522 was intercepted by the F-16s, the F-16 lead pilot reported that there was no visible damage to the Boeing 737 aircraft, that the Captain’s seat was vacant, the person in the First Officer’s seat was not wearing an oxygen mask and was slumped over the controls, and some seated passengers in the cabin were observed wearing oxygen masks. *
It appears to me that the linked video, which is titled "Aircrash Unsolved: The mystery of Helios 522" is taking a lot of liberties with reality to make a dramatic "mystery" where no real mystery exists. The fact that the YouTube account that posted it misrepresents it as an episode of "Air Crash Investigation" is bothersome. The latter show usually does a much better job of being accurate.
* Taken from the AAIASB final report.
I realize this is really not an answer to the actual question. Fooot's answer covers the question very well. This should really be placed as a comment but it is way too long for comments.