alternator warning light

[rb6667]

My warning light never has worked  Knew it was charging since I had 13+ volts at the battery with the engine running.  Now I'm not charging.  10.6 volts at the battery with the engine running.

Looking at the archives (tech manual), it appears that some say the warning light must work for the battery to charge. Others say it does not have to light up to charge.  

Details:

Car has been upgraded( mid 80's) to the internal regulated alternator  55 Amp,   Looks close to the AL74X.  BUT.....the picture shown for the current AL74X looks a little different from the one on the car now.

Would appreciate your actual experience with tracking down my problem.

RB6667

added picture of alternator on car now.

  

[Benz Dr.]

I usually have the alternator and starter gone through when I do an engine rebuild. Most of the time they only need new bearings and brushes. If yours isn't working, take it off to have it tested and the battery tested. Either one, or both, could be faulty.

[garymand]

I see you have the regulator build it to the brush assembly.  It attaches like the connector assembly pictured above but you can see the black regulator that looks like a transistor instead of the connector.  Yours is easy to get to without removoing the whole alternator. 

Repair depends on how thorough you want to or need to be... the bearings usually last a long time unless the belt is over tightened.  They are self greased or lifetime greased.  Its easy to tell if they are ok. They are not difficult to replace.

1) take out the 2 screws that hold the brush/regulator on the back of the alternator.  Careful, the assembly swings out due to the brush springs and the screws are small.  The brushes are probably worn to where one isn't contacting anymore.  The brushes are available on EBAY. I think about $30 or at most auto supply stores.

Then take the belt off and gently turn/rotate the pully while listening to the bearings.  The armature should rotate freely with no bearing noise.  You will hear it and feel it.  Bearings are replaceable and the whole assembly is available new or rebuilt.  Choose your path.

[rb6667]

Thank You Dr and Gary.  I looked back at the repair records I got with this car.  There is a receipt that shows this is a AL80X alternator.  Research shows this was used on the 79-85 300TD.  Good advise on the brushes Gary.  I'll check that out before I take the alternator off the car.

I'm still curious to know if anyone has had this problem before:  Alternator warning light not working, replacing the bulbs makes it charge?

Thanks again.

RB6667

[garymand]

I'm not used to seeing the alternator in that position.  Is it posible it is a retro fit and the wiring for the light was by-passed?

[rb6667]

The  connector for the original voltage regulator is still there just under the overflow tank.  As shown on the picture, the wiring at the alternator has been changed to work with the upgraded  55Amp alternator.   With this in mind, would this cause alternator warning light not to light up?

Many thanks to all that respond.

[garymand]

http://www.ebay.com/itm/new-bosch-REGULATOR-AMC-AUDI-FIAT-FORD-MERCEDES-MERCURY-VW-ALFA-ROMEO-PORSCHE-YU-/121142466055?pt=Motors_Car_Truck_Parts_Accessories&hash=item1c34a75607&vxp=mtr
Heree is what your brushes look like.  I think, yes the light was left out of the conversion.

[rb6667]

Great thanks Gary,  How can I tell if my brushes are bad after I pull this assembly off of the alternator?   What is required to make the alternator warning light work again?  I saw a post by Naj that said something about running a new wire to the upgraded alternator from the voltage regulator connector that is now not used.  This post did not detail.  Here is a picture of my unused connector and again the picture of the wiring at the alternator. 

Any advise much appreciated.

 

[garymand]

I don't know the dimensions, but its more than 1/2 inch new and about 1/4 inch max extension.  Usually one is worn more than the other.  You can feel the brushes compress the springs as you carefully  CAREFULLY SLOWELY push them into position on the alternator.   I guess 1/4 inch is pretty good.  they only cost 35-40$, but this is a new bigger unit that I suspect has not used much brush yet.  The brushes should be good for 100K miles. do you have 100k on this alternator? 

The light is tricky, you need the schematic for the charging circuit and figure out what to connect.  I saw the one circuit but it didn't have the light labels or cross referenc.  If you can find the alternator light in the circuit, follow the wires / colors through the old circuit to the alt.  then rewire yours to include the light. 

[stickandrudderman]

Your light should still work.

[rb6667]

Thanks to all that responded.  Have not had a chance to work on it, but when I do, I'll report back.

Thank You again,

RB6667

[bsimaz]

I was also looking to reconnect my alternator on my w111 220Seb.  Not knowing
which wires went where and finding out that I needed a generator, I opt'ed for
a 'one wire' alternator.   Just mount it and run one wire from the alternator to the
battery.  done.

Not sure how this will effect the warning light but you don't have to worry about
the voltage regulator or any other wiring.

[rb6667]

Update!  I purchased a Bosch Rebuilt alternator to replace the old one AL80X.  One thing I am still not clear on.  This car was converted to an internal regulated alternator in the mid 80's.

  The wiring going to the original external regulator was modified.  My question is was it done correctly?  Please take a look at the picture.  The 2 wires blue and red are connected back to each other.  The original terminal is marked D+   My warning light did not light up when the old alternator went south, and did not light up when the ignition was on but the engine not running. Before I tear into the dash to replace the warning bulb which may be burned out, I wanted to verify that it should work with the current wiring.



Many thanks to all of you for your guidance.

RB6667

[garymand]

Which w113 is this?  Please add it to your profile.

[garymand]

When you turn your ignition switch on prior to start, does the light come on?

[rb6667]

Hello Gary,  I have it in my signature line, looking at my profile, I do not see a place to add that information.  Please tell me how/where to add this.

The warning light has never worked on this 68 280SL since owned by me.  (5 years)   One day I checked the alternator output on a whim, and found it was not charging.  Then I discovered that the alternator had been updated to an internal regulated alternator.

I'm suspicious of the wiring modifications done to the original wiring to make this change. 

Hopeful that some of our members have upgraded their alternators and can explain what changes they made to make the light work.

Many thanks,

RB6667





 

[ctaylor738]

My understanding is that the light (or some consumer) has to come on when the ignition is switched on to "excite" the alternator so that it will charge the battery.  I am not making this up.  There is a blue wire that needs to run from D+ to the ground side of the light.  When the alternator is not turning, it supplies ground to the light.  Positive comes from a circuit that gets power when the ignition switch is on - the diagram shows it as Fuse 2.  When the alternator starts supplying voltage, no more ground, and the light goes out.

You can check this with a test lamp.  One end to positive, one to D+, and start the engine.  The light should go out and the battery should charge.

[garymand]

Good work ctaylor.  Sorry I didn't remembered this thread, sooner.  You are correct:  "When the alternator is not turning, it supplies ground to the light."  May I explain how, maybe someone wants to know how diodes do this?

The ground connection is through the diodes. Diodes conduct in only one direction. When you put a plus voltage on the backside of the arrow and minus voltage on the + side.  ( +<  The diode looks kinda like that.)  You can see in the wiring diagram the back of the arrows on the 3 diodes go to ground on one leg.  With the regulator off, or not working, the diodes willconduct a +voltage to ground.  Current will flow through the dash light along the blue wire then to the red w/black stip wire to the D+.  Then it forward biases the three diodes in that lleg and continues to forward bias the leg that is connected to ground.  If there is + a few volts on the other side of the dash light, it will glow. 

As you said, the other side of the dash bulb goes to ignition switched +Battery (+B). 

So, bottom line rb6667 can test if his dash light is good simply by grounding the small red w/black stripe wire at the alternator