Tach works at low rpm, sometimes

[MarkyMark]

my tach works at idle to low rpms only, and only this only sometimes. As tachs are pretty expensive to, any suggestions where to troubleshoot first? 1994 Johnson 140 in a 23' Hurricane.

 

[HighTrim]

Re: Tach works at low rpm, sometimes

I would start by testing the rectifier as per Joe Reeves instructions in the FAQ. If all is well there, you will need to check the signal source, or simply try a loaner tach with alligator clip hookups to see if the tach itself is fautly.