Jump to content

“L” Light Gremlins!


xderbyx
 Share

Recommended Posts

Okay I’m in need of some help here!

I have been scouring the forum for days looking through threads with info that seems to directly apply to my issue and the understanding of it but I’m falling short.. (wondering if there’s a pun in “short” 🤔)

 

My ‘76 auto has. 320i alternator installed by the previous owner. The wiring harness has been all pulled apart and spliced into numerous times including for this upgrade. The other day I parked at work, and once I shut the car, the “L” light came on and remained on, only shutting once I turn the key to on (and/or start the car). The battery also slowly dies and I’m not sure if it’s the light being on causing this. The alternator does definitely charge the battery too.  I understand that the “L” light is an indicator or the charging system voltage, not necessarily the battery voltage. I did replace the battery as the previous one was old anyway but it didn’t solve the problem, just kinda gave me a new battery lol. I have been trying to test wires for voltage with the car off, but have had no luck other than power towards the hazard switch. 
I’ve read of the “L” light coming on in different manners, probably more in line with voltage fluctuation I’m guessing.. but it’s a pretty straight forward explanation for it coming on only when car is off? 
any thoughts or help is hugely appreciated, I think I’m losing my mind😅

Link to comment
Share on other sites

Something ain't right...The "L" light on your instrument cluster (the L stands for 'lectricity) is fed by two + leads:  one from the battery and one from the alternator.  With the engine off, the light is illuminated by the battery's voltage.  When you start the car and the alternator is charging, then there's +12 volts coming from the wire leading to the alternator; two positives don't make a circuit, so the light goes out.  If you are drawing more current than the alternator generates, then the light comes on dimly as there's more voltage from the battery than from the alternator.   And if the alternator dies, or the belt breaks, the light comes on brightly as it's being supplied only by the battery.

 

That your light is on when the engine is stopped and the ignition is switched off indicates you have a misplaced wire somewhere; the light should go out when you turn the ignition off.  What you have is one of the "joys" of many hands messing with a wiring harness and not documenting what they did.  You'll need to sit down with a wiring diagram and trace all the relevant wires to find your problem.  

 

One thing to quickly check, though:  make sure the alternator is properly grounded with a wire running from the alternator's frame to the engine block.  That's the way they came from the factory; but even if the wire is still there, make sure it hasn't frayed or broken under the insulation or terminals.  An un-grounded alternator can cause all sorts of problems.

 

mike

  • Like 2
Link to comment
Share on other sites

1 hour ago, Leucadian said:

check the ground from the alternator

Yes...this is probably the reason your "L" light is on when the ignition is "off".

You should have only two wires connected to the E21 alternator.

Red from the battery to the B+ terminal.

Blue from the "L" light on the dash to the D+ terminal.

Alternator needs a good ground from the body to the engine block. This was a separate Brown wire on the original alternator which was connected to the D- terminal. The E21 alternator does not have the D- terminal, so must be grounded through the mounting bracket etc.

Link to comment
Share on other sites

5 hours ago, xderbyx said:

...320i alternator installed by the previous owner. The wiring harness has been all pulled apart and spliced into numerous times including for this upgrade...

This (dumbass' doing hack wiring) is the reason I now wear reading glasses due to having to read a wiring diagram for hours tracing wires and reading color codes from the shop manual.   

 

a self regulating alt is nice, but unnecessary on a stock 2002

 

but what do I know. 

 

 

Edited by conkitchen
Link to comment
Share on other sites

5 hours ago, Mike Self said:

Something ain't right...The "L" light on your instrument cluster (the L stands for 'lectricity) is fed by two + leads:  one from the battery and one from the alternator.  With the engine off, the light is illuminated by the battery's voltage.  When you start the car and the alternator is charging, then there's +12 volts coming from the wire leading to the alternator; two positives don't make a circuit, so the light goes out.  If you are drawing more current than the alternator generates, then the light comes on dimly as there's more voltage from the battery than from the alternator.   And if the alternator dies, or the belt breaks, the light comes on brightly as it's being supplied only by the battery.

 

That your light is on when the engine is stopped and the ignition is switched off indicates you have a misplaced wire somewhere; the light should go out when you turn the ignition off.  What you have is one of the "joys" of many hands messing with a wiring harness and not documenting what they did.  You'll need to sit down with a wiring diagram and trace all the relevant wires to find your problem.  

 

One thing to quickly check, though:  make sure the alternator is properly grounded with a wire running from the alternator's frame to the engine block.  That's the way they came from the factory; but even if the wire is still there, make sure it hasn't frayed or broken under the insulation or terminals.  An un-grounded alternator can cause all sorts of problems.

 

mike

 

5 hours ago, John76 said:

Yes...this is probably the reason your "L" light is on when the ignition is "off".

You should have only two wires connected to the E21 alternator.

Red from the battery to the B+ terminal.

Blue from the "L" light on the dash to the D+ terminal.

Alternator needs a good ground from the body to the engine block. This was a separate Brown wire on the original alternator which was connected to the D- terminal. The E21 alternator does not have the D- terminal, so must be grounded through the mounting bracket etc.


the ground that the previous owner had was from the bolt holding the smaller black box (labelled 2.2uf 100V) to the “block” via the nut on the water divider.. I haven’t messed with any wiring personally, but one day I parked and shut the car and *boop* the L light was on. I checked the alternator straight away and *also boop* that very fancy ground wire was broken. I threw a new ground in to a different location cause I didn’t wanna mess with that water divider but maybe since it’s not actually grounded to the block specifically.. ? I will try going back to the block again. 

 

4 hours ago, Son of Marty said:

My guess is a bad diode, allowing battery voltage to "flow backwards" through the alternator to the light with the ignition off, but do check the grounds and wiring before removing the alternator.


I did consider something along these lines as well but didn’t have the working knowledge of the alternator components to back my thoughts. This would call for a new alternator I assume yeah?

Link to comment
Share on other sites

1 hour ago, xderbyx said:

the ground that the previous owner had was from the bolt holding the smaller black box (labelled 2.2uf 100V) to the “block” via the nut on the water divider.

That black box is a capacitor to filter any AC spikes from the output terminal to ground.  It does not conduct DC current.

Edited by jimk
  • Thanks 1
Link to comment
Share on other sites

2 hours ago, xderbyx said:

it’s not actually grounded to the block specifically.

Yes it is grounded...sort of. There is a lot of current flowing from a 65A alternator, and the water divider is not up to that.

You need a big wire (10 AWG) from one of the alternator body bolts directly to the block. Don't connect it tp anything that has a rubber bushing at the mounting point(s).

  • Confused 1
Link to comment
Share on other sites

Does anyone have a picture that they’d be willing to share of where the factory ground is actually going to from the alternator? This way I know for sure it’s a working ground location.. and John76’s recommendation of 10 AWG wire.. is that the factory spec?

 

sorry for the specifics but this dude had a terrible 16ga wire going from the capacitor mounting screw to the water divider and I never had a problem until it just decided to break lol

Link to comment
Share on other sites

1 minute ago, xderbyx said:

10 AWG wire.. is that the factory spec?

 Yes.

 

The wire simply goes from one of the studs/nuts that holds the two halves of the alternator body together over to one of the little bolts that holds the timing chain cover on.  The ground stud on the alternator is slightly longer than the others on the alternators I have.

 

(My computer died and took 400 gigabytes of photos with it, so I don't have access to them right now.  Luckily, I saved them but I have yet to move them onto this computer).

 

Tom

  • Thanks 1
Link to comment
Share on other sites

4 hours ago, '76mintgrün'02 said:

 Yes.

 

The wire simply goes from one of the studs/nuts that holds the two halves of the alternator body together over to one of the little bolts that holds the timing chain cover on.  The ground stud on the alternator is slightly longer than the others on the alternators I have.

 

(My computer died and took 400 gigabytes of photos with it, so I don't have access to them right now.  Luckily, I saved them but I have yet to move them onto this computer).

 

Tom

Excellent Tom thanks a bunch! I’ll give that a try and see if that solves the problem. 

Link to comment
Share on other sites

A bit hard to see in my photo. Used the bolt/nut on the alternator body and connected it to the alternator bracket bolt with a 10AWG wire. I also kept the big Brown factory wire for good measure.

The alternator really needs a good ground, and so does the original voltage regulator on the fender wall (if still used).

 

alternator ground - Copy.jpg

  • Thanks 1
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...