I have a 1998 lincoln town car and it is not charging when running. Below is what I have done/tested.
- replaced alternator with a reman from rockauto. After replacing and still experiencing the same problem I took the reman alternator to autozone and it tested good.
- battery tested good.
- the 2 wire plug on the back of the alternator broke during alternator replacement. I ordered a new pigtail and soldered the wires to the existing harness, correctly matching the old plug
- using a test light with the key off, one of the pigtail wires is hot; when I start the car the other wire also turns on
- the charging system fuse (number 13 under the hood) was blown. It was replaced. Of note, I drove the car for 2 years with the battery light on and never had any trouble.
- the battery light on the dash comes on when keying on, after replacing the fuse 13 it goes out once the car is started
- I can start the car without the pigtail plugged in. When plugging in the pigtail while running I can hear the alternator pull down. If I apply a load to the battery via a battery tester, while the car is running, I can hear the alternator pull down even further.
- with the car running I used a voltmeter to test voltage at the back of the alternator and found it equal to what I was seeing at the battery (12.6v)