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Re: 86 9kt battery light stays on Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Mon, 10 Sep 2001 09:25:43
In Reply to: 86 9kt battery light stays on, Ronald Wainwright, Sun, 9 Sep 2001 18:12:52 Members do not see ads below this line. - Help Keep This Site Online - Signup |
The battery light on means that the Alternator isn't charging the battery. This isn't a battery problem - it's something with the alternator.
The 11.8 volts you saw means that the alternator isn't putting out current. Replacing the battery will do no good.
Here's some questions - With the old alternator, was the battery light on all the time? On the back of the alternator, there are two wires - the thick red one from the battery, and a thin (yellow?) one. That wire is supposed to connect to the field coil post on the alternator. The field coil post is just a screw connection on the back, but it's insulated from the alternator body, which is ground. If you tie the yellow wire to the alternator body (ground), the battery light will be on all the time, and the alternator won't charge the battery.
One reason why I asked if the battery light was on all the time before is if that yellow wire is shorted to ground anywhere, the light will be always on and the alternator won't work. When you first start the car, current flows from the battery, through the light, and into the alternator. Since current is flowing through the wire, the battery light is on. Alternators have electromagnets (field coils) inside, so they take power to work. That current energizes those electromagnets. Once the electromagnets are working, the alternator starts producing its own current, and it takes over the job of powering the electromagnets. So the current through the yellow wire drops to zero, and the battery light goes out. This normally happens in a second or two when you start the car. If the yellow wire is grounded, the battery light will be on all the time, and the alternator will never energize the electromagnets, and will not charge the battery.
A few other possibilities - did the rebuilt alternator come with a voltage regulator, or did you re-use the old one? The voltage regulator is a diamond-shaped device bolted on the back of the alternator. My guess is that the rebuilt came with one, but it's never safe to assume. When an alternator is bad, most of the time the problem is the voltage regulator, not the alternator itself.
Two last items - do you see the alternator pulley turn? If the serpentine belt is loose and slipping, the alternator pulley won't turn, or won't turn fast enough, and you'll see the problems you're seeing.
Lastly - how do you know the rebuilt alternator you bought was good? Even brand-new factory parts come through dead on occasion. If the yellow wire is tied to the proper place and not shorted to ground, AND the alternator pulley isn't slipping on the belt, I would suspect the 'new' alternator or voltage regulator.
Good luck, and keep us informed!
posted by 140.157....
, Mon, 10 Sep 2001 09:25:43 <-- Viewing This Message
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