Hrm, wish I'd seen this one a bit earlier. It does sound like you're having some confusion about how the 7's exposure controls work,whether or not the camera's good. With the 5's you get more-conventional old style controls, but that's part of why they cost more on the used market.
I wonder if the Sears lens isn't responding properly on A cause the automatic's for Ricoh?
Maybe I can help clarify for photolady:
The AF switch on the side of the camera's lens mount there (on all models) *only* relates to autofocus. Totally independent of exposure or exposure mode. Once you get the rest sorted out, you can choose between auto and manual focus as you like without affecting anything else.
You generally set what exposure settings your exposure mode gives you control of by the toggle around the shutter dial, (for one, you hold a button down while doing this) all with the lens set to A.
Av mode is 'aperture priority' ...this as you may recall, lets you choose the aperture and the camera will set the shutter speed. I believe with this camera, you can leave the lens on A for this and set the aperture with the toggle around the shutter button.
Sv is 'Shutter Priority;' here you choose the shutter speed, and the camera will set an appropriate.
P is 'Program,' that's fully-automated exposure.
M up on the mode dial is for manual. This is the setting you want for manual. With the lens' aperture ring set to A, you should be getting aperture info in the finder: those -- lines probably mean the camera can't communicate with the lens, I believe.
If you put the mode dial in P and the lens' aperture ring on A, you should see both shutter speed and aperture if the lens and camera are talking OK. (Oh, wait, there is no P on the dial, let me see what you should do. You can use the smiley face 'Green' mode for now or one of the picture modes with the funny symbols. Let me be sure how you do that. Looking at an online manual now)
(Here is where you can find the manual online: this should explain things for you, too.
http://www.butkus.org/chinon/pentax/pentax_mz-7/pentax_mz-7.htm)
Aha. I think I found the problem: under the section for manual exposure: "When lenses other than an F or FA lens are used, no aperture information will be displayed in the viewfinder." (That's a little annoying, but it means your camera probably isn't broken. )