How do you get past the four levers and gate in Harmugstahl?

When you arrive in the room, all the levers should be up. If they are not, it won't work, so you need to either load your autosave game from when you entered the area, or try to exit the area and enter again, until you have them all in the correct position.

If the levers are all up (so opposite you, pointing to the corridor), if you number the levers 1, 2, 3, 4 starting from the left when facing the corridor (so 1 being the left one, and 4 being the right one), you should pull 1, then 2, then 4. Wait around one second between each pulling.

You have the procedure shown here and here.