Possible bad alternator?
 

Hi all. I have an 02 Crown Vic that I think the alternator is going bad. The battery reads 12.6v at rest and between 13.85 and 13.9v at idle. When I start turning on accessories the voltage starts to drop- depressing the brake pedal and putting the transmission in gear the voltage drops to about 13.7, turning the blower on it drops to 13.5, and turning the steering wheels it drops to around 12.6 and sometimes down to 12.4v. Could this be signs of an alternator going bad? The alternator is original with 138,000 miles.

It might be a good idea to have the alt output checked to confirm it is putting out what it is rated at. Some voltage drop is normal, but I would still like to know for sure that the alt is capable of delivering what it should.

To do a bad alternator check, unplug the negative cable from the battery while the car is running. If the car dies then your alternator is bad. So if your car still runs while the battery cable is unplugged then your alternator is fine. A little trick I found is very useful to save yourself 50-60 bucks.

The procedure of removing a battery cable worked with a DC generator, but is not recommended with an alternator. Without the battery in the circuit the alternator has no load and can self destruct.