Connecting the tachometer......

Got an 89 Cavalier with the 2.8 MFI engine. I dropped a rebuilt engine in it which seems to work fine except for the tachometer. When I'm cranking the engine to start it, the tach reads about 500 RPM which is about what I'd expect. After it starts, the tach goes all the way over the top and pegs at about 9000 rpm. Since I can hear the engine is idling, there must be a connection loose somewhere. I suspect its a green wire I've got "left over". This green wire comes out of the same harness that the oxygen sensor comes out of, but for the life of me, I can't find out where to plug this wire in. Any one got any suggestions? It seems related to the tach problem, I just can't find a fitting to plug it into.

Greg