Alternator problem ?


Old 10-27-06, 12:15 PM
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Question Alternator problem ?

If I don't use my Ford 1990 CV for a few days, the battery discharges and I have to put on the charger to get it started. I traced the leak to the alternator: there is a roughly 120mA current going from the battery to the alternator battery terminal (+B) at all times (car not running).
Took the alternator to have it checked and they told me it is working ok. Shouldn't there be only a minimal current or none at all going from the +B terminal to ground?
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Old 10-27-06, 12:26 PM
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Have you tried replacing the battery?

Of course there will be juice in the cable that comes off that battery, at all times. There is no switch on the battery to shut the juice off.

Also, disconnect the battery for a few days and test the voltage, etc. If it loses to much where u can start it, that means a bad battery.
Old 10-28-06, 07:15 PM
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I certainly checked the battery before I removed the alternator and performed the test, which I did using a 12V power source on my work bench and not the battery.
Old 10-28-06, 07:45 PM
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Are you talking about from battery to alternator terminal or from the terminal to ground?

If the shop tested the alternator for charging capability and it showed OK, your problem isn't likely in the alternator.

To run down a battery drain, we would disconnect the ground to the battery and insert a test light from the cable end to the neg post. Move all the wires around you find to see if you can trip the light off. If nothing there, go to you fuse box and start pulling fuses one at a time. Replace them before you pull the next one.

Keep in mind you may have some parasite drains like a clock. Pull those fuses first.

Usually one of them will trip the test light off.

Good luck,

Hope this helps,

Old 10-28-06, 10:22 PM
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dude, autozone raped me over this one.

My 68 gto did the same thing.
They said the alternator was good, 3 different times!!!
Yes it did charge. But the diode(s) inside the alternator were blown. When the car was shut off, current flowed from the battery+ , through the alternator, OUT of the alternator to ground. Would kill the battery if it sat 2-3 days.

I went back to autozone and pointed this out to the 3 employees, including a manager and he said their machine did not test for bad diodes.
I was LESS than sympathetic as I pointed out all the hours spent looking for a short in the circuit.

As others stated, and sounds like you've done-
Disconnect your battery ground wire.
With EVERYTHING shut off,(pull radio fuse if clock stays on), door shut - no interior lights etc, there should be NO current flowing in the system.
Hook a 12 volt bulb between the battery GROUND wire and the frame. If the light comes on, the is a short SOMEWHERE in the system killing the battery. Mine stemmed from the alternator diodes. You say you have traced it to the alternator - get the diodes tested or just replace it. I did - it solved my problem.
Good luck
Old 10-29-06, 05:32 PM
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Thanks to all who responded to my post.
When I wrote that I traced the leak current to the alternator, I meant to say that I checked all the wiring, pulled all the fuses, etc, and still had a leak until I unplugged the connector on the alternator, which stopped the current from flowing to ground. Then removed the alternator from the car and, on my work bench, applied + 12V to the Bat terminal on the alternator and connected the negative to my meter and then to the alternator housing and I measured the same leakage current.
It seems that it is exactly the same thing that happened to 95sse. What I didn't know is that the test setups at the parts store don't check for leaking diodes. I will get a new alternator tomorrow.

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