Grimrock

The wooden door to the southern section of the lightning corridor won't open.
I found the 3 switches to get the secret plate boots, etc.
There is a lever in that same room that is supposed to open the southern door but it doesn't work.
Is there some other switch involved.
Thanks for any help

it opened a door further east (and south), and in there is a way to open the southern section door

thanks. got it