alternator charging then stops at high rpm

[brm0525]

Hello all. New to the forumn. I have just recently joined after getting many helpfull threads.
Here's the issue. Just bought 21' 1988 sea ray seville with a mercruiser 4.3 alpha 1.
Alternator charges on initial start up then as rpm inreases it stops charging. Also seems when engine gets up to temp it also stops charging. Had alternator load tested at marine supply store checked out fine. Replaced battery and still not charging correctly. Please anyone help with any info would be appreciated.

 

[Eric 3.7LX Alpha 1]

Re: alternator charging then stops at high rpm

Using digital multi meter. Test the alternator terminals when this happens. The ignition power wire to the alternator will be purple. If the alternator is not receiving power from the ignition switch then it isn't going to generate power.

If that purple wire checks ok, then test the output terminal at the back of the alternator.

 

[Bondo]

Re: alternator charging then stops at high rpm

Hello all. New to the forumn. I have just recently joined after getting many helpfull threads.
Here's the issue. Just bought 21' 1988 sea ray seville with a mercruiser 4.3 alpha 1.
Alternator charges on initial start up then as rpm inreases it stops charging. Also seems when engine gets up to temp it also stops charging. Had alternator load tested at marine supply store checked out fine. Replaced battery and still not charging correctly. Please anyone help with any info would be appreciated.

Ayuh,.... Welcome Aboard,.... What info are ya basin' yer assumption on,..??

Voltmeter,..??

Ampmeter,..??

Multimeter readin',..??

 

[brm0525]

Re: alternator charging then stops at high rpm

Using digital multi meter. Test the alternator terminals when this happens. The ignition power wire to the alternator will be purple. If the alternator is not receiving power from the ignition switch then it isn't going to generate power.

If that purple wire checks ok, then test the output terminal at the back of the alternator.

I will do that. Now I'm checking the purple wire at the alt side or the switch side? I did have the alt tested on bench. Are you saying to test the orange wire in place while running to see if it duplicates what's happening at the battery?