"L" Light stays on

[lobf]

Hi folks- 

 

I've been chasing electrical problems in this car for months now, and just when I thought I had them mostly sorted, I have a new problem with my L light not turning off. 

 

My car got booked on a TV show a week ago, and when it got back they told me they had to jump it, and my voltmeter was reading too low. 

 

When I went to look at my connections, I saw they had all been shaken off, so the alternator wasn't connected at all. 

 

After reconnecting everything, I ran it, and the "L" dash light stays on. Reading the current at the back of the alt shows 12.15 volts, it used to show ~14. 

 

I took it to my alternator repair shop, they tested it and said that it was working fine, that it *should* be showing about 12.5 volts at 68 amps.

 

I told him that it should be 14 volts at 80A but he said that it was charging fine according to their machine. 

 

I asked them to replace the regulator anyways to see if that solved it, but it didn't. I got it back today and they insisted that if my "L" light stays on it's something else besides the alt. But it used to put out 14 volts! I'm confused. 

 

Not sure where to go from here. I recently replaced my dash lights with LEDs, could that be causing the problem? From my understanding of the current, as long as that "L" light comes on for a minute when starting the car, I've given the alt the jump current it needs, so an LED shouldn't cause a problem but who knows. 

 

Edit: I should also mention that this is a Bosch AL46X, internally regulated alternator that I bought a few months back, in order to "reduce issues" with the external voltage regulator. It has reduced no issues so far ?

 

Edit 2: According to this article "If instead the voltage stays at 12.6 volts with the engine running, or the light doesn’t go out, or both, and you’ve checked all the connections I’ve described, then either the voltage regulator is bad—it’s likely stuck in the bypassed configuration—or the alternator is bad. You need to figure out which one it is. It could be both." That was in reference to the stock alternator, but that shouldn't make a difference right? Is this truly the only possible answer? I've used this alt shop for years, they're total pros, could they have gotten something wrong when testing?? 

https://www.bmwcca.org/roundel/bmw-2002-charging-system-diagnostics

Edited February 17, 2021 by lobf
addtl info

[Schnellvintage]

Check your ground strap to the block and chassis.  Also (many times overlooked) the alternator housing is grounded.  All should be corrosion free and free of paint at connection.

 

 

[lobf]

I'll check the big ground strap. Not sure what your comment about the alternator housing means- however I am grounding using the alternator housing, and connecting that to the block. Is that an issue? It isn't according to the alt shop 

[2002iii]

What TV show?

 

Any correctly functioning alternator should put out at least 13.5v. I would try disconnecting the battery with the engine running, if the alternator is functioning properly it should make enough power to keep the car running.

 

What else has been done to the car recently?

[lobf]

Not sure what show, it was a pilot. If it gets picked up I'll find out and let you all know! 

 

As far as recent work, besides a paint job, I've just been trying to clean up and chase down electrical issues. The turn signals stopped functioning so I've been trying to track down a new 9-terminal stalk (since I can only find the 6-terminal version) and I rebuilt my center console, adding an oil pressure and a voltmeter gauge, plus a clock. Pretty small electrical additions there, and I feel pretty good about the wiring job back there, despite being a bit ugly. 

 

And I thought so too, so why would my (very experienced) alternator shop tell me that you can't pump volts and amps at the same time, that the alt was charging, and that 12.5ish volts was to be expected?? 

 

 

[2002iii]

13 minutes ago, lobf said:

Not sure what show, it was a pilot. If it gets picked up I'll find out and let you all know! 

 

As far as recent work, besides a paint job, I've just been trying to clean up and chase down electrical issues. The turn signals stopped functioning so I've been trying to track down a new 9-terminal stalk (since I can only find the 6-terminal version) and I rebuilt my center console, adding an oil pressure and a voltmeter gauge, plus a clock. Pretty small electrical additions there, and I feel pretty good about the wiring job back there, despite being a bit ugly. 

 

And I thought so too, so why would my (very experienced) alternator shop tell me that you can't pump volts and amps at the same time, that the alt was charging, and that 12.5ish volts was to be expected?? 

 

 

Since the car was recently painted I would check all the ground connections to the body.

 

Might try disconnecting the new gauges and clock just to rule them out.

 

I don't know why any reputable alternator business would tell you 12.5v is good. Did they test the alternator on the car? I would take it to another shop. Most Autozone's will test an alternator off the car for free.

Edited February 18, 2021 by 2002iii

[Son of Marty]

Your ground strap from the alt to the block should be the same size as the alt output to the battery. I would think that the led warning light doesn't have enough resistance and that might be why you aren't getting to 14v.  

,

[lobf]

37 minutes ago, 2002iii said:

Since the car was recently painted I would check all the ground connections to the body.

 

Might try disconnecting the new gauges and clock just to rule them out.

 

I don't know why any reputable alternator business would tell you 12.5v is good. Did they test the alternator on the car? I would take it to another shop. Most Autozone's will test an alternator off the car for free.

This is probably the most reputable alternator shop in LA- I’ve been independently referred to them a half dozen times. They’ve done a bunch of great work for me in the past. 
 

I guess I need to contact them again in the morning. No, they didn’t test it in the car, I pulled it and drove the alt down to them in my girlfriend’s car. They put it on some machine but yeah I think maybe they were just wrong. 

[lobf]

30 minutes ago, Son of Marty said:

Your ground strap from the alt to the block should be the same size as the alt output to the battery. I would think that the led warning light doesn't have enough resistance and that might be why you aren't getting to 14v.  

,

Ground wire never changed, and I tested the ground point so I know it’s still a functional wire. 
 

Why would resistance play a part in getting the jumpstart current to the alt? As long as the circuit completes, it’s fine right? 
 

On that note, I was getting a bit over 2 volts on the D+ (jump start / L light wire) line, is that the correct amount? Not enough to trigger my test light but detectable on my voltmeter. 

[2002iii]

22 minutes ago, Son of Marty said:

Your ground strap from the alt to the block should be the same size as the alt output to the battery. I would think that the led warning light doesn't have enough resistance and that might be why you aren't getting to 14v.  

,

Yeah LED's do weird things to older cars. Try putting a regular bulb back in.

[lobf]

Wow I MIGHT have just answered my own question regarding the resistance on the L light line. 
 

I just manually bridged B+ and D+, I heard the alt engage, I’m getting 14 volts, and my L light is off. 
 

That means there isn’t enough current on D+, and I’m assuming that is related to the dash light being replaced with an LED. 

 

How do I find the original incandescent bulbs for this? Like what is the form factor called so I can pick up a freshie in the morning and test if that’s the issue? 

[2002iii]

3 minutes ago, lobf said:

Ground wire never changed, and I tested the ground point so I know it’s still a functional wire. 
 

Why would resistance play a part in getting the jumpstart current to the alt? As long as the circuit completes, it’s fine right? 
 

On that note, I was getting a bit over 2 volts on the D+ (jump start / L light wire) line, is that the correct amount? Not enough to trigger my test light but detectable on my voltmeter. 

Only 2 volts wouldn't be enough to light a regular 12v bulb, like the one in your test light. LED's can operate on Lower voltage than they ate rated for. So the LED is probably part of the problem. 

[2002iii]

9 minutes ago, lobf said:

Wow I MIGHT have just answered my own question regarding the resistance on the L light line. 
 

I just manually bridged B+ and D+, I heard the alt engage, I’m getting 14 volts, and my L light is off. 
 

That means there isn’t enough current on D+, and I’m assuming that is related to the dash light being replaced with an LED. 

 

How do I find the original incandescent bulbs for this? Like what is the form factor called so I can pick up a freshie in the morning and test if that’s the issue? 

BMW-07119905358

[lobf]

 Do you know where I can find incandescent bulbs for that cluster? Or what they’re called?  
 

edit- sorry just saw the next post

Edited February 18, 2021 by lobf

[Son of Marty]

I haven't followed the circuit deep enough to figure how the resistance of the bulb effects the field circuit, but I do no that if the bulb is burned out or removed you'll get no power to the field and no charging. I think 12.6v at 68 amps is a reasonable reading your 80 amp rating is most likely be at 12.v and under ideal conditions on a good day downhill with a tailwind situation and up amping any alternator in the same size case is going to cause more heat which will decrease output. As my aircraft electronics instructor was fond of saying "you can pass 1 million volts at 1 million amps through a wire smaller than a human hair, you just can do it for long".