Erratic Tach Readings

I own a boat with twin 1993 Merc 200's. Recently, my port tach didn't move upon starting and then began giving erratic spikes. I replaced the tach with a new one. Same problem with new tach. What’s next on your list of diagnostics? I was told it is likely a voltage regulator problem. Any advice would greatly help. 

P.S. the engine runs fine at all rpm's. I just can't synchronize it with my starboard engine without a tach reading




Sounds like the rectifier is bad. Have that checked first. This is the 1” by 1” square item right above the switch boxes, but to the rear of the starter solenoid. 

I would think this would fix it. If not, look at the grey tach pulse wire. It could have a bad section. 




Please submit whatever questions you have to  All questions and answers selected will be displayed on this page as they come in.  Note: though all boaters are welcome, priority may be given to I.H.R. members.  Randy can not be held responsible for any advice given.  Though his information and expertise is second to none, he has no control over what you do with your boat.  It is up to you to boat safely and act responsibly, and his advice is only to be used as a guidance for your high performance boat/motor of which you are the one responsible for the risks involved.

Mark C.


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