Spoilers: Lever Location for Mission 4

[Xuhybrid]

So far the levers have been fairly easy to find along with the secret retro levels that they open. However on the Argent Facility (Mission 4), i spent about 30 minutes hunting for it without any luck. It's the only thing i have left to find and i don't like moving on unfinished.

Google results are not returning much yet as it's early days, and the only hints i have found are very poorly explained;

http://segmentnext.com/2016/05/13/doom-classic-map-levers-locations-guide/

I tried restarting the level to get back into the spawn area (which is locked for some reason) but there was no luck finding the lever there either. Has anyone gotten this lever yet? The door is surrounded by satanic circles and bodies dripping blood. I just can't find the lever!! Help me!

[Xuhybrid]

Finally found an answer; (found before the satanic room)
http://steamcommunity.com/sharedfiles/filedetails/?id=683971786
http://www.gamefaqs.com/boards/819505-doom/73732305