Thanks for the suggestions all. With ground disconnected from the battery and small ground wire disconnected from the body, I am still getting voltage when I touch the neg post to the neg wire. Disconnectin the alternator had no effect, so I guess it probably has something to do with the starter, or maybe the strap that is grounded on the engine block. This is with nothing connected to the negative post at all.

I am going to pull the starter today or tomorrow and check the grounding strap as well as the starter. I think I remember seeing a procedure for testing the starter several different ways in the Chilton's manual. I replaced the contacts a few months ago and found that one was badly corroded. Maybe the corrosion caused some other damage, causing my current problem.

Any other thoughts or suggestions you all might have would be appreciated!