Tachometer Died

[peterpagnott]

I have a 2003 merc 150 Saltwater series. I was out the other day and the tach seemed to be reading 1000 RPM to high. After about 20 minutes it started working correctly again. As soon as I was thinking it was a loose wire or something, the tach quit completely. Is thier a book I can buy to find out how to research this problem. Any ideas on what the problem is????<br /><br />Thanks

 

[Silvertip]

Re: Tachometer Died

Start the engine (in water or on muffs of course) and measure the voltage at the battery at about 2500 rpm. Only a short burst is necessary. If you are reading 13.2 to about 14.6 volts the regulator is working and its likely the tach that died. If you read battery voltage (12.6V or less) the regulator/rectifier has gone south. Since the tach sense signal comes from this component, the tach won't work. Also, if the voltage is 15 volts or higher, that says the regulator is damaged and must be replaced as well as it no longer regulates charging voltage and since those are high output alternators, can overcharge batteries. As always, make sure all battery cables (both ends) and tach connections are super clean and tight and that you have no wiring issues before replacing expensive parts.

 

[Silvertip]

Re: Tachometer Died

Start the engine (in water or on muffs of course) and measure the voltage at the battery at about 2500 rpm. Only a short burst is necessary. If you are reading 13.2 to about 14.6 volts the regulator is working and its likely the tach that died. If you read battery voltage (12.6V or less) the regulator/rectifier has gone south. Since the tach sense signal comes from this component, the tach won't work. Also, if the voltage is 15 volts or higher, that says the regulator is damaged and must be replaced as well as it no longer regulates charging voltage and since those are high output alternators, can overcharge batteries. As always, make sure all battery cables (both ends) and tach connections are super clean and tight and that you have no wiring issues before replacing expensive parts.