Tach Question

[maineiac5586]

I Have A 76 Merc 500 And The Tach Is Not Working Properly. The Tach Won't Read Above 3000 Rpm, But It Works Ok From 1000 To 3000. I Assume The Motor Is Revving Higher Than This Because When I Give It Full Throttle It Seems To Go Into Its Powerband And Plane The Boat. Boat Is A 16 Foot Duranautic. Speedo Shows Top Speed Of 29 Mph. Sound About Right?? Can I Replace The Tach With A Newer One And If So, Are Wires Compatible On Tach?

 

[jimg984]

Re: Tach Question

could be a shorted recetifier, this where the tach sending wire connects, the recetifier changes the ac volts to dc volts

 

[maineiac5586]

Re: Tach Question

where is this located?

 

[maineiac5586]

Re: Tach Question

also noticed battery is only getting 12.3 volts at idle and when motor is idled up in neutral.

 

[jimg984]

Re: Tach Question

look for two yellow wires coming from under the flywheel attaching to it, the brown tach wire will attached to same place as one of the yellow wires

 

[maineiac5586]

Re: Tach Question

problem solved, replaced rectifier, tach now works and battery charges thanks!!!!

 

[sc00ter78]

Re: Tach Question

Was the rectifier difficult to remove?

I think I need to replace mine, will be testing it this comming weekend. I can't find my service manual.

 

[maineiac5586]

Re: Tach Question

piece of cake, it was located above switchbox to the left of starter