150, inline 6, tach question

[bones1]

Hello<br /> I have a 76 inline 6, Merc. Runs great, but<br />tach is erratic. Shows idle, but on top end varies. The tach says thunderbolt ignition on<br />back. But what is confusing is that the black<br />wire connection has a +, when diagram indicates<br />ground. The back of tach only has 2 connections.<br />It did work last season.<br /> Also, can I use a newer tach on this engine?<br /> Thanks ahead, Joe

 

[mellowyellow]

Re: 150, inline 6, tach question

welcome aboard,<br />first check the connections at your rectifier.<br />thunderboldt ignition does require a special<br />tach, but there are aftermarket replacements.<br />I like "tinytach" for about $40, but am sure<br />teleflex has one too along with other mfgs.<br />does yours plug into front of control box?<br />if yes, check for bad wires in there also.<br />good luck,<br />M.Y.