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'06 Town Car - Intermittent Battery Light, alternator and battery test OK

My charging system warning indicator is coming on intermittently. It’s been doing it for ~3,000 miles and doesn’t seem to be getting worse. Battery and alternator have both been pulled and tested and both are checking out fine. I think I’ve tested all of the connections and grounds and haven’t found any that seem to be loose. The only thing i can think of, which may be pure correlation, is that I replaced the stereo with an aftermarket head unit shortly before the problem began. So my two questions are:

  1. What else can I check?
  2. Could something in the stereo head unit wiring be creating enough electrical draw to set off the light? The stereo’s never shown any signs that something’s afoot, but ya never know.

There’s two signals from the alternator connector that the pcm monitors. Wire colors are Ye-LB and Ye. The other wire is the thick Ob-Lb one that goes to charge the battery. You may have a loose connection in those two wires somewhere between the alternator and the pcm.

Start by doing the basic diy’er alternator test first. Before first start of the day the battery should measure about 12.6 volts. Immediately after starting the engine it should measure 13.5-15.5 volts.

When the light comes on see if turning other electrical equipment on and off makes any difference, including the stereo. For the stereo try turning the volume up and down too. Measure the voltage at the battery at the same time. If the voltage drops unexpectedly, you’ve found a major clue.

Its more than likely the brushes inside your alternator reaching the end of the line… They will lose contact with the armature and cause the charge light to flicker…till they give up the ghost entirely. Or I suppose it can also be another component inside the alternator.

The batt/charge light only illuminates when the system does not detect a charge state from the Alt… so it is happening intermittently for now… it will soon stay on and you will replace the alternator. The test performed just caught it on a good day…with no vehicle movement or real world vibrations.

In my Crystal Ball I see a new alternator in your future also money fame and power, however I can only guarantee one of those items in that list.


Thanks! Once the polar vortex moves out I’ll get under the hood and give it a peek.

You’re probably right, but don’t crush a man’s dreams!

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I agree it’s most likely brushes.
I don’t know how easy it is to replace just the brushes on this domestic make.
It was easy on a couple Hondas I used to own.
Brushes in a plastic holder that screws on.

I remembered that the alternator that was on there had a lifetime warranty, so I took it back to the store again… and their bench tester was broken so they warranted the alternator and I put a new on in. On the way home the light came back on so i jumped out and tested the output at the terminals with my meter whole the light was still burning on the dash and it was bang on 14v, so now I’ll start tracing wires

Sounds like you are getting the situation under control. If you measured 14 v at the battery w/the engine running and the alt warning light was on, most likely there’s something wrong w/the alternator warning light circuit, not the alternator. I think on your car the alternator warning light is turned on by the pcm, based on its input of the battery voltage and the signals on those two wires I mentioned above. So your idea to trace those wires out from the alternator to the pcm seems like a good one. This may eventually require specialized equipment that a shop would have to figure out, but I think you are on the right track. You can always get a pro diagnosis then do the repair yourself if you like. Best of luck.

just curious, what version of ford alternator does your Lincoln use? 3G?

Should be this one:

I wasn’t able to track down any wires that seemed to be the culprit. Called a local Ford dealer and talked with one of their service guys about the symptoms and what I’d done so far. He said the most likely thing is the PCM is having problems since everything else seems to be working normally. Guess I’ll have to take it to a (shudder) dealer for service

I had a 98 crown vic ( essentially the same car ) that tripped the battery light & that the alternator tested “good” 3 weeks later it crapped out. I would change the alternator and see the light go away.

I replaced the alternator on Saturday. The issue persists. The voltage tests normal even when the light is actively burning on the dash

So that simply suggests that the voltage sense wire is either broken and making intermittent connection or the plug that snaps into the alternator has female terminals that are hollowed out and not making good connection to the light on the dash.

Look into those culprits first… The alternator plug is one of the things that has been constant throughout all these alternator swaps…check that each terminal connector is healthy inside that plug and or the wire responsible for voltage sense.

Another idea, since everything is working except for the dash warning light, just put a piece of black tape over the dash light. The downside is if the alternator really does fail you won’t know it. but there may be a work-around-for that. try googling, see if there’s a circuit you can rig up using the two wires from the alternator that will turn on an led that you install on the dash somewhere. The way that circuit works I think is one of those wires is from the ignition switch, and the other is from the voltage regulator on the alternator. If the ignition switch wire is 12 volts (key in on) and the voltage regulator wire is 0 volts (engine not running) the light will turn on. if the ignition switch wire is 12 volts (key in on/run) and the voltage regulator wire is 12 volts (indicating the engine is running and the alternator is outputting voltage) the light will turn off.

It might be as simple as this
------------------------------- vvv 12 volt LED (new warning lamp)
ignition switch wire … ------->---- voltage regulator wire

Note that the dash light problem may have nothing to do w/the alternator or its wires/connectors. And it might have nothing to do w/the pcm. It could be a problem on the dash panel itself, just something shorting out making that light turn on.
BTW, if you are using the Ford 2G alternator, good idea to upgrade to the 3G version. Unlikely to be the case in a 2006, but worth checking. Ford had some reliability problems with the 2G version.

I seem to have fixed the issue and the culprit was… the alternator. It seems that, against all odds, I managed to get 2 bum alternators back to back. So after replacing the original alternator in August, the replacement 5 days ago, and the replacement replacement this morning the issue seems to be fully resolved.

I’m reminded of the castle in a swamp from Holy Grail: but the fourth one stayed!

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Thanks for letting us know.

Your experience with rebuilt or cheap new alternators is not unusual, based on what I’ve read here for years. I would much prefer a used OEM one from an auto recycler, or to take mine to an auto electrical shop and have them diagnose and repair and test it.

Sometimes time demands getting one locally right away, but that has its downside, too.