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1999 Ford Taurus bad alternator?

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Dec 26, 2007, 6:01 AM

Post #1 of 3 (2100 views)
1999 Ford Taurus bad alternator? Sign In

While I was driving my radio and lights were going down and up like the alternator couldn't keep a charge up. Went and had the alternator tested and they said it was fine, but when they tested it they wanted everything off, is that normal.

Two days later I was driving home half way there the lights started diming shut all electronics and lights off and battery light was on, continue driving for another 30 minutes when the car died and would not start. I think it is the alternator but not sure. Could the voltage regulator be an issue?


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DanD profile image

Dec 26, 2007, 8:05 AM

Post #2 of 3 (2096 views)
Re: 1999 Ford Taurus bad alternator? Sign In

Yes it’s normal to turn all accessories off while testing an alternator; an external carbon pile (loading device) is used to apply load too lower system voltage. By doing this there is less of a chance of hurting the accessories with a voltage spike.
It shouldn’t matter as far as the charging system is concerned, how the battery voltage is brought down during a test. By lowering system voltage, the regulator should trigger on and allow the alternator to begin charging; in an attempt to maintain a minimum voltage of no less than 12.5 volts but not exceed 15.5 volts.
The regulator is built into the alternator and it’s not uncommon for the alternator or regulator to have an intermittent fault. So likely what happened when they tested the system is it was working “normally” then; you drive the car down the road and hit just the right bump, under hood temperature or load on the system and it/they decided to shut down?
Here’s an easy test you can do on your own; it won’t tell you how much the alternator is producing, just that it is producing something.
Have the battery fully recharged; then connect a voltmeter across the battery terminals. Take a reading with ignition off; should be around 12 - 13 volts. Start the car; after a couple of minutes take another reading of the voltmeter. You should see an increase in voltage of two - three volts; with a reading of no more then approximately 15.5 volts. Over charging a battery is just as bad as an under charged.
You could also start turning things on, headlights, heater fan, rear window defog ect. See if battery voltage remains in between 12.5 and 15.5; you may need too increase engine rpm to approximately 2000 rpm.
Like I said this won’t tell how much the alternator is charging but if the voltage stays in the above mentioned range it’s charging enough.


Canadian "EH"

Double J
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Double J profile image

Dec 26, 2007, 1:14 PM

Post #3 of 3 (2091 views)
Re: 1999 Ford Taurus bad alternator? Sign In

just for kicks... have had a couple of these recently where the belt tensioner was worn enough as to not keep tension on the belt...causing a discharge concern/light on....stall out ..Cool
just a thought...something to check ...
all tho in this case ,i agree with dan...sounds like the alternator failed....good luck

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