the "L" light

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eso

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Hey everyone im new in the e9 car scene. I just got my 72 cs about a month ago. It runs great, but the other night I parked it and the "L" light stayed on with the car off. I went and did some research and found that this is a light for the alternator. I thought that it was strange because it turns off when the car is running. Anyways went out in the morning and it had drained the batt. Im not sure what is going on but now the electric fan is always running when the car is on, it only ran when the motor was getting hot before. The L light continues to stay on, could it be a relay with the fan? Thanks
 
The red alternator light should only come on when the ignition is on. It is normal for the light to turn off when the alternator is running, the strange part is that comes on with the ignition off.
Do any other systems come on with the ignition off?

Not sure if the electric fan is related to that, do you have AC? Is the AC switch off?
 
eso said:
no other systems are on when the car is off. I have ac but the switch is off.
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Wow, where are you located? I'd love to look at the wiring on that car. You may need an exorcist more than an electrician.
 
L Light

I would suggest you have your alternator looked at. You probable have a short circuit in the diode area.
K D
 
hmmm

this is an odd one!

When you say "the electric fan stays on" is that the fan in the center console, or something else?
 
Is this the aux fan in front of the radiator & AC condenser? If so, maybe the thermostatic switch in the radiator (IF you have one of those) is malfunctioning to always on, and IF your fan is wired to bypass the ignition switch, or your ignition switch is going out, it could keep running after you shut down...

Charlie P.
 
Ya its the electric fan in front on the radiator. the fan does not run when the car is off but it will start running as soon as the car is started. do you think that if I have a short in my alternator that it would keep the light on? Or could it be the relay that is connected to the alternator via little brown wire?


Thanks, Spencer
 
I took off the wire on the the back of the alternator and now the "L" light has turned off when the car is not running. does this mean that the alternator is no good?

Thanks, Spencer
 
You just got love owning an old car...It took me 10 years to figure out why my 68 280sl would not start on the first try.
Good luck, I look forward to seeing the solution to this problem. I put my money on the ignition....maybe a bad connection or something. Alternator is easy, just take it out and take it to a autopart where they can test it.
abe
 
I don't know about the alternator, but I think there's something funny with the fan. If you have a thermostatic switch in the bottom of your radiator where the hose attaches (my '74 has this) that controls that fan, and it sounds like you do because you said it used to come on only when hot, then try disconnecting the wire from the thermo switch. That might tell you something useful.

Charlie P.
 
Has this been seen/resolved by anyone else? I had the same problem show up today. Assuming I have a short somewhere but not sure where to look.

L-light turns off when I turn the key over to on.
Acc, off and key out L light stays on.
Battery : 12.2v while off

7073095F-B97C-4156-9276-766CCD4064E2.jpeg
 
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OTOTOTO said:
Has this been seen/resolved by anyone else? I had the same problem show up today. Assuming I have a short somewhere but not sure where to look.

L-light turns off when I turn the key over to on.
Acc, off and key out L light stays on.
Battery : 12.2v while off

View attachment 109828
Click to expand...

Check the wires on the back of the alternator & could be a faulty regulator.
Do you have the owner's manual or Blue Workshop Books?

 
Starting with the wiring basics will eliminate the simple issues. Remove, clean and/or replace the battery cables, do the same for the alternator groundwire (this should go from the alternator to the engine block), make sure the contacts for the multi-plug to the alternator are clean and wires are solid, check the other end of that multi-plug connector at the voltage regulator also. Definitely replace the battery cables if they are hand-made cables with the clamp-on terminals. And, use heavy gauge wire for the alternator ground.
 
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Use your voltmeter to determine if your alternator is leaking Battery positive voltage at the D+ connector. Pull fuse 6 to see if that circuit is giving you your ground
 
No change with pulled fuses but I have chased it to the cable running to the alternator. The voltage regulator is warm to the touch after being parked for 2 days which I assume is no bueno.

Got it unplugged and battery on trickle charger for now since it’s been drained a bit the past few days.
 
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The three wires from your regulator are in a plastic sleeve, open it up and your wires are probably bare and shorting out, this is very common. I wouldn’t charge anything until I examined the wires.
 
@adawil2002 I think this conversion has already been done, the external regulator location is blank. Not sure what went in the 3rd slot. The part that was warm is the internal one. Pics below.

@HB Chris I should have mentioned, battery if off the car. So far haven’t found anything super frayed besides some shrink missing from the coolant temp wire.
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16B76121-C6B3-4896-BC74-806BCF7A567C.jpeg
 
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