Charging System Warning Light dimly lit in gauge cluster

midniteliquid · Post by **midniteliquid** » 22 Mar 2013, 11:24

Good day Gentlemen!

I have had an issue over the last little while with the Charging System warning lamp being dimly illuminated (only really noticeable at night). The dimly illuminated warning lamp has also been accompanied by an increasingly dragging starter.

At first I suspected the battery, but having replaced it just last year I suspected the alternator as the culprit. I got out my multimeter and tested the battery voltage with the car off. It measures 12.5 volts. I tested the voltage feeding into the battery at idle by connecting the test leads to the battery cables; it measured 13.3 to 13.5. Seeing that this voltage is low, I connected the positive multimeter lead to the nut where the alternator to starter cable fastens on the back of the alternator, and the negative multimeter lead to the negative battery cable; it measured between 14.5 to 14.8 volts. This led me to believe the problem might be in the cabling between the alternator and the battery. I connected the positive test lead to that same nut on the back of the alternator and the negative lead to the positive cable feeding into the battery; it measured between 0.92 and 1.0 volts.

My conclusion is that the cables between the back of the alternator and the battery are causing around a 1 volt drop which is slightly impeding the battery's charging ability, and resulting in my gradually flattening battery and the dimly illuminated charging system warning lamp.

Is my logic here flawed? Am I on the wrong track?

As always, any input or wisdom from you gentlemen is greatly appreciated!

Thanks!

-Brandon

Post by **mikealder** » 22 Mar 2013, 11:50

Your logic is good for half of the circuit, the poistive side, I would also be checking the engine earth straps and main battery negative connection to the chassis as these could easily show the same issue - Mike

Post by **cn90** » 22 Mar 2013, 11:55

The diode in the alt is probably going out.

Post by **JDS60R** » 22 Mar 2013, 11:58

Yes,
Always assure grounds are performing first. If grounds are fine then:
Replace suspect alt lead. If its creating a 1 volt drop its well past its life. If you are going to make up a high grade replacement you can find parts on the web including www.remybattery.com

Post by **jimmy57** » 22 Mar 2013, 12:22

Reading that difference between charge output and the D+/61 lead (skinny wire blade terminal on alternator with red/white wire) is the sign of failed rectifier diode leg. You've lost 1/3 of alternator capacity. The high voltage on D+ lead is the result of voltage regulator overdriving the rotor in alternator to make up for the failed leg of alternator circuit. You're seeing the 1.5 volt diff between D+ and the 13.3-13.5V in electrical system on the other pole of that light bulb. If you check the output lug on back of alternator for AC voltage you'll find .3 V AC or more (>300 mV) which indicates diode failure. The old way to check for this would be an oscilloscope pattern of the alternator but that only shows you the excessive AC voltage not converted by rectifier diodes which is detectable by AC voltage check.
Time for an alternator.

Post by **JRL** » 22 Mar 2013, 14:44

ALL these cables are going bad now after 11-14 years.
With 99 and 2000s the B+ cable goes bad and on 98-2000 the positive cable can go bad.

Before you replace the alternator, check these cables and ends
(I have a very good (off of a 2000) alternator for sale...cheap)

You can visually check the B+ by opening the fuse box and look where the cable attaches.
If the brass strip is burned or corroded, it's a VERY good chance it needs replacing.
A PIA job, everything including the battery has to come out, it runs under everything.

As for the positive cable 90% of the time, just replacing the cable end at the battery does the trick

Post by **jimmy57** » 22 Mar 2013, 15:15

Yep, I re-read and found he did not check D+ but was actually doing Vdrop on B+ cable the long way in the first statement.
Results in alternator light dim for voltage difference between D+ to bulb and B+ to bulb but for different cause than failed rectifier diode leg.

midniteliquid · Post by **midniteliquid** » 23 Mar 2013, 18:54

As always gentlemen, thank you for your input. It is very, very much appreciated!

I replaced both the cable from the back of the alternator to the solenoid, and the solenoid to the positive post of the battery with brand-new 2 ga. cables. I noticed an instant difference! The starter cranks like it's fresh out-of-the-box, every single light in the car is at least 60% brighter, and the car seems to have much more power than it did before.

I can't believe how bad the cables had gotten!

I now measure no more than a 0.05 volt drop from the charging cable connection on the back of the alternator, to the positive terminal on the battery. I went ahead and replaced the negative cable as well as the two grounding straps off the back of the motor with new heavy-gauge cable. It seems to have made all of the difference in the world.

Should I go ahead an do the B+ cable to the fuse box as a matter of course also?

Thanks again for your help!

-Brandon

Post by **jblackburn** » 23 Mar 2013, 21:49

If the rest were that bad, I'd go for the B+ too. That's a common weak point on the 99-2000 models.

Good to hear that it wasn't the alternator, though!