1999 Ford Taurus - Alternator Problems? Please help!

My 1999 V6 3.0 Taurus wouldn't start. I took the battery and alternator to get checked. They were both bad and I replaced them both. I just put in the new alternator and the battery light is on in the vehicle. I also tested the new alternator by removing the negative cable from the battery while the car is running. The car died. I checked the connections on the battery and they all seem to be snug and clean. I also rechecked the battery connections and they were tight. What would the problem be? Any ideas?

In short, replaced batter and alternator but battery light is still on.

You may have gotten a bad alternator. Did you buy it at O'Reilly? They're well known for selling faulty rebuilt starters and alternators! Otherwise there could be an electrical short, but i'm not familar enough with engine electrical systems to make a diagnosis.
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The test by removing the battery cable and the car stalling is not recommended on modern cars, and can actually cause damage to the electronics. So I'd say that test is inconclusive. The battery acts as a large capacitor and filters a lot of the alternator's noise before it gets on the electrical system. The alternator produces AC, which is then rectified and filtered by the battery to provide a DC signal to the car. When you open the circuit to the battery, the unfiltered noisy rectified signal makes it to the PCM and other electronics which may react unpredictably.

Do you have a voltmeter to check what voltage is on the battery when the engine isn't running and also when the engine is running? If not, you can pick up inexpensive meters at many of the department stores, hardware stores, of if you're really looking for an inexpensive one, Harbor Freight has them. To do much more troubleshooting of the charging system you're going to need a meter.

I trust you've also double-checked the connections at the alternator. You'll also want to check fuse 26 (30A) in the Engine Compartment Fuse/Relay Box.

-Rod

I check the fuses. There was a 20 amp fuse that was bad. But it wasn't the problem. I put another 20 amp fuse in it's place and the battery light was still on. I'm about to go and get a voltmeter. What should the voltmeter reading be? Also I checked the alternator connections last night and rechecked them this morning. They are tight and they are clean.

check your ground cable and wires

I can't see inside of the 30A fuse. But I'm just going to replace it. I also removed the alternator and took it back to Shucks/Oreilly just to have it tested. It tested fine. I will check the ground cables. The other wires look fine..Any other ideas?

At the battery the voltmeter on the DC scale should read 11.90 to 12.5 volts when the engine is off. As you start the car, the voltage should not drop below 10 volts. With the engine running you should see between 13.4-14.4 volts if the alternator is working properly.

-Rod

I did the voltmeter test. The battery when the car is not running is 11.77 and the battery when the car is running is 11.20. I replaced the 30A fuse. I also replaced a 20 amp fuse. I replaced the battery and the alternator (which I just had tested to make sure it worked right). I also checked the battery ground wire. And it is secure. The wiring to the alternator seems fine at the connections. What should I do now? Any ideas on the culprit?

check to make sure you have 12v at the alternator.

The alternator is fine. Checked that. Could be mega fuse????

It was the mega fuse! Got it! It was a $5 piece! Thank guys for all your help!

Where can I buy a mega fuse? I tried Autozone, and they are not listing it.