I have 3 vitessas, 2 T's (without the barndoors) and a L, the coucing lever should stay down with the doors shut, but does not always due to the age of the camera, and the plunger is both a cocking and film advance plunger, one press should advance the film and set the shutter, as to what you call the frame advance wheel, I dom't know what your mean, the only wheel on mine is on the back, near the viewfinder and that is the rangefinder wheel, so you should have the shutter release and cocking/advance lever on the top and on the back near the viewfinder there should be a wheel for the rangefinder, which moves the lens as a unit via moving the bellows in and out when you close the barn doors then the lever should press down into the top and lock plus the shutter release button should also push down into the top, perhaps a previous owner released the barndoors and opened the camera without a finger on the plunger so allowing the plunger to spring up and clonk into place, which in the instructions Voightlander warned against as it can damage the plunger, you must control the rise of the plunger with your finger to prevent it clonking into place, that is all I can think of that can cause a problem, check if the film counter is turning when you press the plunger, if it does the you should be able to use the camera as is, if not then it needs a small repair,