Chevrolet: Chevy Caprice, chevy caprice, speed buffer

Question
I own a 1992 Chevy Caprice and my Speedometer doesn't work. So I notice that I didn't have a Speedometer Vehicle Speed Buffer, I found one at a junk yard and I plug it in and it worked. Then I park and left my car and when I returned and started my car the speedometer didn't work? What could be the problem? It worked the first time and now it doesn't?

Answer
Hi Patrick
        I mostly give help with the 1955 thru 1975 cars , but I would say that the sending unit or sensor for the speedometer must be bad it sounds as it burnd out again ,
can you follow the speedomometer cable/wire and see what is in its path and check for juice , did any fuse blow .