1998 Merc 150 rebuilt. My tac suddenly doubles it's reading- wired properly-any

[tarponator]

My 1998 Merc 150 was recently rebuilt. Engine running good and have recently finished break in. Lately the tach reads approximately double of actual RPM. Then sometimes it gets back to "near" normal, but I don't beleive it's correct. Any Ideas?<br /><br />Thanks for your time.

 

[tarponator]

Re: 1998 Merc 150 rebuilt. My tac suddenly doubles it's reading- wired properly-

Re: 1998 Merc 150 rebuilt. My tac suddenly doubles it's reading- wired properly-

I researched older forums and read the following "Make sure your battery is charging..Above 13 volts. Tachs that starts acting up are the first indication of a charging system problem (they are connected electrically)."<br /><br />Is this true? I just noticed one of my batteries is not holding a good charge and was going to replace. I put both batteries on the charger last night. When I get home, they will be fully charged, if the tach begins reading normal. well there you go....I'll let the forum know my results...