alternator output and battery charge

[yimmyb]

I now have a different issue. Boat starts and runs fine but charging system is messed up. I purchased an alternator that matched the number off the old one. When engine is running it was putting out 28 volts. Took it back and was told it had a bad regulator. Got it replaced and installed and the new one is putting out 18 volts. Also it pegs my voltmeter and does not seem to be charging the battery. The wiring is orange, red/purple, purple and black. it is a 1980 mercruiser MCM260

 

[Bt Doctur]

standard output is 14.6 ,more than that and the alt is defective The red/purple and purple are just the sense and excite leads .Without them there is no output. black is ground but the mounting bolts supply that too. A loose/missing black wire wont do it.
How are you measuring this voltage

 

[bruceb58]

Measure with a multimeter at the output of the alternator. Do not trust the gauge at your helm.

 

[yimmyb]

Taking measurements at the alternator output{ large orange} terminal. The voltmeter and volt gauge read the same voltage. The large orange wire is currently running up to the dash and is not connected. I am not sure if the batteries are charging or not. Maybe I have the wrong alternator which is giving me an above average output. Thoughts?

 

[Bt Doctur]

Well, that a good reason for it to run wild and not charge. Remove that orange wire and run a new wire from the alt directly to the starter for testing

 

[bruceb58]

Curious...was their ever an ammeter used on this boat? If so, it may have been disconnected and a voltmeter put in its place by someone who didn't know what they were doing.

 

[yimmyb]

I am not sure if there was ever an ammeter installed. It had a voltmeter when I bought it. As far as I can tell the large orange wire spits above the alternator. One goes to the cutout switch, one down to starter solenoid and the other up under the dash. I will run a wire from the alternator to the starter.

 

[Bt Doctur]

One goes to the cutout switch, one down to starter solenoid and the other up under the dash. I will run a wire from the alternator to the starter.

The output should just go directly to the battery post on the starter, it may go thru a 90A plastic block .no cutouts, no orange to dash, etc

 

[bruceb58]

As a quick test, just run the output to the positive battery post.