I've been trying to troubleshoot the charging system in my daughters 2000 Eclipse, 2.4l-4, auto, 90k miles. About 2 weeks ago, the CHG snd BRAKE warning lights came on. I connected a voltmeter to the battery and determined that the alternator was not charging. Replaced w/ rebuilt, started it up, no warning lights, voltage at idle 13.5; thought that was fixed. The next morning I get a call saying that the CHG and BRAKE warning lights are coming on dimly, and only from idle up to about 1500RPM. Also, turning on accessories (headlights, a/c on high, etc.) at idle would extinguish the lights. Thinking I got a bad rebuild, I exchanged that alternator for another. Same exact symtoms with the second one. Decided to have her drive the car for a while and see what happens. It appeared the battery was staying charged for the first week, then a couple of days ago, the behavior of the lights changed. They were now lighting up from idle to about 2500RPM, and turning on accessories no longer extingushes them. I monitored the voltage as I took the car around the block and it does appear that the alternator is not charging anytime the lights are on, and barely charging some of the time that they are off. I checked the battery (1-2 years old) with a hydrometer and all 6 cells are showing about 75% charge. Checked connections near the battery, cleaned some grounds etc,; no change.
Does anyone know for sure if it's normal for the BRAKE warning lamp to illuminate anytime the CHG warning lamp is on? Looking at the circuit diagram, they have a pair of diodes in the instrument cluster that are wired in such a way that makes me believe that this is normal. The circuit diagram is available here on pg. 90-35 for anyone willing to load it. (it's a 14Mb PDF, sorry)
My next thought is to connect a voltmeter the Powertrain Control Module under the dash and monitor 5V and ground leads that run to the alternator. Maybe cleaning/reseating the plugs on the PCM will help?
Sorry for the long post. All recommendation welcome.
Jim