I've got a 97 Taurus 'U' motor that has had an alternator problem for a while, but now it's getting worse. The car has 110,000 miles on it. At first, the battery light would come on and the headlights would dim if you brought the motor up to 4,500 rpm. I noticed that the belt tensioner was approaching the low limit indication, so I changed the belt. No help. Lately, the light has started coming on at 3,800 RPM. Last night I was coming home (I'd been driving about 4 hours) the motor was turning about 2400 rpm, and I started noticing the headlights going a little dim and then coming back to normal. I slowed down a couple of MPH, and everything was fine. Sped back up, and it started again. About 1 1/2 hours later, I was almost home and pulling away from a stop sign and the charge light came on @3,000 rpm.

Obviously I've got something failing in the alternator, but does anybody have any idea of what?? When the belt didn't fix anything, I thought the alternator field windings might be opening up at high rpm. But it's been doing this for 20,000 miles, so that probably isn't the case. I saw 1 additional case of this on the web, but that was in an F-150, and received no responses.

 

sounds like the brushes in the alternator are worn to much

 

What David paul said...Plus

Easy way to check is to hook a Digial Volt Meter up to your battery, start the vehicle and watch the voltage. Should go up to about 14.5vdc and then settle down to about 13-13.5vdc. Then turn on everything you have...Radio, A/C, fan on HIGH, headlights, high beams and if an extra person is available have then step on the brakes.

Voltage should go up to about 14-14.5vdc. Then while everything is "ON", have the extra person run the RPMs up to the 2500-3000 RPM range. You should see the voltage starting to drop out on the DVM.

Time for a new alternator.