40 hp outboard tach gauge stopped working

[jonathanteller]

I think its year is around 1980 or so. The tachometer stopped giving a reading and there is no output from the wires coming from the the alternator (where they join the battery). The battery is not charging ie. if it starts with a reading of say 12.4 volts with motor off.....it (the battery) stays reading 12.4 volts with motor running. Do i have a bad alternator

 

[jonathanteller]

Re: 40 hp outboard tach gauge stopped working

I'm thinking that its the regulator/rectifier unit that's bad . Thats a $70 part and easy to change out. Only that I have four wires and the new part comes with an extra red wire?? Where could that go?