I have a 2000 Ford Focus LX. I bought it used with high miles (162K). Since I have had it, the alternator/battery warning light has been on. I recently replaced the alternator and the light still stays on. Alternator checks out fine. Since replacing the alternator I have notice that when the vehicle is cold the light goes off for about 15 miles, however, when this happens, the headlights pulsate. I have seen in chats there are many electrical issues. Any suggestions on this one?

 

Usually the pulsating is caused by a voltage regulator problem. Not serious , but annoying . Depending on how the alternator was checked may not show the voltage regulator problem. Best cure is a Ford remanufactured alternator. You may notice that many times I suggest rebuilt starters and alternators from a Ford dealer. All alternators are not the same even with the same model car. If there is a starter / alternator rebuild shop locally, they should be able to correct the problem with your vehicle's alternator. It is best to wait until your original alternator is repaired . Then everything goes back together quickly.

I am sorry to say that I am not positive as to whether the computer controls the output for your Focus' alternator. Will try to get the answer for that.