Battery charging question

[walkinfool]

My car's charging system works most of the time though occasionally, the L light will appear after I've started the car and the battery won't charge. This will happen if the battery is low but sometimes that's not the case and the car is just being finicky and the charging system will roar to life after driving the car for 5 or 10 minutes.  I might add that my car spends a lot of quality time in the garage during the rainy, winter months and the battery can become drained. So, after repeatedly borrowing my neighbors trickle charger, I finally bought one of my own. Both times after using my new trickle charger to charge or top off the battery I have discovered that the L light will come on and remain on even after a 10 minute or longer drive. But, if I wait a few days for the battery to run down just a bit I can start the car and the L light will go out immediately and then I hear the reassuring yet faint "whirring" noise the car makes when the alternator is charging the battery.  It’s as though the battery needs to be less than fully charged for the charging system to function. Does that make sense? I haven't yet checked the system with a multi-meter but suspect there could be a defective voltage regulator or a problem with the alternator or voltage regulator wires/plug? Any thoughts on this?  

[Dudeland]

Check the voltages and report back.  Not much we can say without that. 

[Simeon]

Remember, the L light is effectively a ‘tug of war’ between the battery and the alternator. If either gets a significantly higher voltage than the other then the bulb glows. In the case described, the freshly charged battery could be a higher voltage than being output by the alternator.

 

Take some voltages (at the battery with the engine off, with it on and seemingly charging and with it running and seemingly not charging). 

 

Short answer may be that hat there are problems with voltage regulation. Do the easy things first and check all the terminals on the alternator and regulator (if you have a separate one) and check that there is a reasonably large (6mm2) ground wire between the body of the alternator and the engine. 

 

Do that and report back what you have found. 

[Mike Self]

Your problem could be...

1.  A sticking regulator--presuming you have the original alternator with an external voltage regulator--it's electromechanical and has a set of points inside; they can stick, especially from disuse in a damp and humid climate.

 

2.  Wiring plugs on the regulator and alternator may be loose or corroded.  The one on the back of the alternator is supposed to have a wire bail to hold it in place; this is often missing and will allow the plug to loosen without it being noticeable.

 

3.  The big red hot wire (under a rubber boot) on the back of the alternator is loose, or corroded.  All the alternator's juice flows through it.

 

4.  The alternator's ground wire (alt case to block) is missing, corroded or has partially separated from the terminal on the block end--this is almost unnoticeable unless you examine it closely.  

 

Or...

5.  Your alternator (and or regulator) may be in the throes of dying...

 

Let us know whatcha find...

 

mike

[walkinfool]

Thanks all for your helpful suggestions! I do have the original alternator with external regulator. The wire bale is still in place and keeps the plug firmly attached to the back of the alternator. I'll check all connections, ground wires, and voltage this weekend and report back! Cheers, Mitch.

[PaulTWinterton]

 

2 hours ago, mike said:

4.  The alternator's ground wire (alt case to block) is missing, corroded or has partially separated from the terminal on the block end--this is almost unnoticeable unless you examine it closely.  

 

 

My first thought.

 

The symptom is usually a perpetually dim L light.  Detach that wire and the L light is bright.

 

[walkinfool]

Thanks Paul. My L light is either out completely when the system is charging (along with the faint whirring noise that I can hear) or strong and bright. I've never had a dimly lit L.  

[foreste2002]

I had my 74 tii alternator rebuilt locally years ago and the light kept staying on....I replaced it with a rebuilt Bosche unit and the light stayed off and charging worked again....I had the problematic unit autopsied and they said it had "bad diodes" and a standard rebuilt would not have fixed it.....not sure if this info helps, but there it is.


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[worzella]

From the FAQ articles. I do not see your case specifically but might give you some ideas. 

 

I was in denial when I had an alt prob using a brand new rebuilt Bosch. Finally dropped another $80 for one more and problem fixed

 

But I think I cooked my diodes when installing first one ?

 

[walkinfool]

Hello again. Voltage at battery while motor off and when on, not charging was about 12.2. Couldn’t get the L light to go out this weekend during long drive so no charging voltage available. All connections including ground were secure. I pulled the voltage regulator and though the guts seemed clean, there was some pitting on the points so I may buy a replacement regulator and see if that fixes the issue. Otherwise, it may be time to replace the alternator. Thanks again for your thoughts!

[Mike Self]

Try cleaning the points on your regulator with an ignition file or a doubled-over piece of 100 (or so) grit wet/dry sandpaper.  That'll clean up dirty points; if that doesn't help, then try a new regulator.

 

mike

[walkinfool]

Update: Thanks again to all who weighed in. I was convinced after checking everything that the voltage regulator was the culprit but made one more round of plug/wire checks to make sure I hadn't missed anything. Also, before installing the new regulator, I pulled the existing one and cleaned up the pitted points. Turns out that the ground that attaches to the plug behind the alternator was loose (even though it looked like it was attached) and after reattaching to the connector and securing back into the plug, the charging system was back to working as it should. Cheers, Mitch

[landon]

I think I jinxed myself by saying these cars are reliable in another post..... though this may be just operator error.

 

Out for work today and used the headlights going thru a tunnel. Forgot to turn them off. Made a couple of stops, the last one being about an hour and a half. Started the car fine and drove back to the office. The car ran out of electrical after about 20 miles on the highway. Checked voltage at the battery and saw 7 volts. The L light never came on. Okay... got a tow. While waiting, the battery regained some charge - up to about 11 volts. By the time I got home we had 11.3 volts and it was able to start again. Running voltage was the same 11.3 volts. Not seeing any L light when ignition switch is on or when running. Swapped out a good bulb and can't see any L light. 

 

I'm going to take the battery in for a check tomorrow and charge. It's still only showing 11 volts. Grounds look nice and clean. Alternator and voltage regulator are high mileage - 130k and 15 years old. 

 

Is this simply a dead battery? 

Check the D+ circuit?  Seems like coincidence to have a charging failure.....  

 

Thanks for your thoughts.

 

[Son of Marty]

I think it's a dead alternator, what is your alternator output voltage?

Edited October 14, 2022 by Son of Marty

[2002iii]

Sounds like your alternator died, but could be wiring and/or battery.

 

You can have autozone check your battery and alternator for free.

 

Check all the alternator wiring and battery cables for looseness and/or corrosion. Sometimes the corrosion is hidden inside the insulation.