The RED L light won't go out when car off

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fast3.0csi

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After working on the car today I noticed after I turned the car completely off and removed the key the red light in the cluster with a L will not go out. When I start the car it goes out. Any suggestions? Thanks. 1972 3,0csi
 
That is the alternator light and should not be on when the key is removed, it can only be on when the ignition switch is in the Drive position (III) or Start (IV).

It goes off when you start because the alternator is working.

You ignition switch may be at fault or somebody messed up the wiring.
 
Sounds like you are bleeding battery + to pin 5 at connector k.
Disco the voltage regulator first and then big green spade connector at the fuse box.
Check for battery voltage at the green wire when disco'd to see if it is the switch.
 
The connector that carries positive battery voltage to the L bulb from the fuse box.
Green and green/white are the positives to all the warning lights.
Only when a ground is present does the circuit complete.
Only the Alt light is different- the Alt changes from a ground to a positive when it runs.
 
Arde said:
You ignition switch may be at fault or somebody messed up the wiring.
Click to expand...

The bulb will glow regardless of which direction the current is flowing. So:

1) As Arde writes, the ignition switch may be delivering +12 to one side of the bulb even when it is off. However, if that were the case, then other electrical components would also be on. Does the parking brake indicator also glow with the lever pulled up? Do the gauge needles register? If not, then the switch probably isn't the culprit.

2) The ignition switch may be fine, but the alternator may be sending +12 to the other side of the bulb. Recall how the bulb glows briefly when you turn off the key, as the alternator keeps putting out voltage and the components connected to the key'd circuits serve as the ground. Well, that could be going on all the time with a defective alternator or regulator. Is your charging system working OK?
 
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the alt is charging, I install dial volt gauge I getting 13.5 running. The battery glows bright when the car is off only, running it goes out. I also noticed when I turn on the heater blower the voltage drops to 8 to 10 volts. when I turn off the blower goes back to 13.5. I upgraded to the internal regulator alternator with the black box mounted on the outside of the alternator.
 
sounds like you have a short or ground issue - could be a circuit is grounding itself by running thru the gauge light - which probably means that it is feeding itself by running upstream looking for a ground.

i am not a pro at this, but starting with a little background - the charging light is first fed from the alternator and voltage regulator and connects to fuse 6. (so unless you wired up the new alternator / regulator wrong ...)

in looking at the diagrams and a desire to keep thoughts simple - i think you might have power flowing thru the light switch or the ignition switch. first check fuse 6 (with key off) - is there power there - on either side? the light switch is powered directly from the hot side of fuse 4 (unswitched - straight from battery) it connects to light switch at pin 30 w/ red wire. and leaves the switch and goes to fuse 6 (green wire - pin 15 on switch). so my guess is that power is flowing thru the switch and powering fuse 6. if so, there are 2 ways - bad light switch or bad ignition switch. so try unplugging the light switch and see if the charging light goes out. if that doesn't work - try unplugging the ignition switch (which is fed from fuse 5 - which is bridged to fuse 4 on the hot side).

it is doubtful that power is flowing upstream from the unpowered side of fuse 6 - but if you don't have luck with the above - you can remove the fuse and see if the light goes out.
 
It is more likely a fault is causing 12V to appear at the L lamp while the ignition switch is off and follow a path to ground through the alternator stator winding than a reverse path fault that requires the diodes to be shot in the alternator and also a short to ground when the ignition switch is off. One fault vs two.

That is my bet. If the wiring is not original, my bet is off, you need an exorcist.
 
Arde said:
It is more likely a fault is causing 12V to appear at the L lamp while the ignition switch is off and follow a path to ground through the alternator stator winding than a reverse path fault that requires the diodes to be shot in the alternator and also a short to ground when the ignition switch is off. One fault vs two.
Click to expand...

Arde: Your second scenario, with the +12 coming from the alternator, does not require a second fault; what you describe as: "short to ground when the ignition switch is off." The ignition switch powers a number of devices including the charging indicator. So if the alternator side of the lamp is powered, its other leg has a great path to ground through all of those resistive loads. Sure, there is some resistance but it is fairly low with multiple, parallel paths to ground. Perhaps the lamp glows a little dimmer than it would with the key on and the alternator off, but it still can glow plenty bright.
 
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Right the coil would be a path to ground.
In that case diodes are more likely to fail than the ignition switch.
I change my answer with the same conviction as before.
 
is there normally power to fuse 6 with the key off? i don't see any supply to fuse 6 + 7 with the key off or the lights off. sure there is a lot of stuff across the fuse, but its not powered until there is a supply from the switch. if there is power at the lamp, then there is probably power at fuse 6 ... and it has to get there somehow. unless i've missed something on the wiring diagram - ordinarily without the lights on or the key on, there shouldn't be power at 6. my point is to rule things out.

its been a long time since i took out the old alternator and separate regulator on my old bavaria and replaced it with the newer style ... but i remember i had to change the wiring for the regulator. i might still have the diagram, but i'm sure there are enough people that have done that change to know what to do. but if its not done correctly that could create a power issue to the light with the key off ... as it is in-line. i am taking the presumption that it was done correctly and looking for other alternatives.
 
Disc the blue wire- light out means diode is bad
Light on- you got a short
 
Or even less work, if the L light turns OFF with the ignition in Run mode (but not started) then it is the alternator diodes. If it stays ON it is a short.
 
disconnect the alt lead

I disconnected the main lead to the alternator and light went out, when I connect it the light comes on . Do I have a bad Alternator or regulator? Thanks
 
Diode is short instead of open- it happens pretty often.
 
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