Strange alternator issues

[kyle_in_rure]

Hello all,

A little over two years ago the replaced the alternator on my 97 4.6 Expy because it was not charging 90% of the time. It left me stranded after about a week of having issues with keeping the battery charged.

Now I am having a strange problem. When i first started it up in the morning to go to work (in the dark), I noticed the headlights are dim, wipers slow, etc. it was like this for the first 20 minutes of the drive then magically started acting normal again. It has done this every day for the past week. I checked the voltage at the battery posts when I was noticing the dim lights and it was a solid 12.1 volts (not high enough, right?) and when it starts charging again it is around 14.1 volts. The trouble is I’m not sure where to start looking first. Is this an alternator issue or some kind of regulator issue?

Also I noticed the battery light in the instrument cluster is burned out, so if it should be coming on it obviously isn’t.

Thanks!


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[stamp11127]

Check the plug that connects to the alternator and also check the output wire terminal where it bolts onto the stud.

Check voltage between the output stud and alternator case then next time you are having the issue. Charging voltage normally runs between 13.5 - 14.5 volts. If it isn't charging with that test the field coil isn't being energized. That can be from a faulty plug, coil or voltage regulator.

 

[kyle_in_rure]

Hi stamp,

Before I got the chance to do any investigating, it kicked back on today while driving and was making a loud whining noise. This makes me think it’s on its way out... what do you think?


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[kyle_in_rure]

Also, strangely enough, the battery light is illuminating again when I turn the key to run but don’t start it. Seems weird to me that it appeared burned out before....


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[stamp11127]

Could be going out. Doesn't say much about the alternator brand if it only lasted 2 years.

 

[kyle_in_rure]

Yeah I agree. Could the battery light acting up have anything to do with the alternator itself?

I was reading on some sites where the battery light sometimes helps form the charging circuit and the alternator won’t charge without it. Strange


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[stamp11127]

Not to my knowledge. It provides a current path when the alternator isn't charging. That passes current through the bulb and illuminates it.

 

[1955moose]

On my Lincoln mark 7 that was the case. It has to have a functioning bulb and circuit for the charging to work. If it were me I'd clean all connections involving charging. Like stamp said, its most likely either the regulator inside alternator, or alternator itself going south. But eliminate all your connections first. If you can find one, new alternators work better than remans. They rarely use quality diodes on most remanufactured units. Let us know what you do

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[Big Brian]

I dont know what kind of alternator you got but I dont mess around with rebuilt or reman units.

Only new for me. May cost a little more upfront but worth it in the long run.

 

[stamp11127]

OK, got the book out. Some alternators do not have residual magnetism to start the process of generating electricity. These alternators will send current to the field coil through the light bulb and create the magnetic field needed to start the current flow when the ignition key is first turned on. After it is running it uses some of the electricity generated to power the coil and extinguish the light.
So if the bulb burns out, the coil doesn't get energized initially and the result is no output.