FYI, a rectifier going bad or already bad will cause the tach to go crazy or not work at all. Take a look at the rectifier to see if its ever over heated. You will see black tar like stuff running down the outside and maybe some overheated wires that connect to it.
From Genesis: "And God promised men that good and obedient wives would be found in all corners of the earth."
Then He made the earth round...and He laughed and laughed and laughed!