Stupid lgen light question
- birddog1148
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Stupid lgen light question
My generator light is staying on. It's a '69 so it was a generator car but has a '73 externaly regulated alternator. The volt meter shows between 12 and 15 volts depending on the engine RPM. This is pestering me. The battery seems to be being charged so why the light? And I had another '73 alt and engine in the car before this and the light didnt stay on so thats why I think I have it wired right.
- Leatherneck
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Re: Stupid lgen light question
Have you put a multimeter on it yet?
- CentralWAbaja
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Re: Stupid lgen light question
I don't remember exactly but it seems that there is a wire from the alt back to the light that once energized it cancels the original voltage that is lighting the light?
I may be way off...it's been like 16 years since I wired my car
I may be way off...it's been like 16 years since I wired my car
It is not Mickey Moused.....It's Desert Engineered!
- Leatherneck
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Re: Stupid lgen light question
Did you just install this or is this a new problem?
- Big Dave
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Re: Stupid lgen light question
If the wire to the gen (alt in your case) is shorted (grounded out) it will cause the light to stay on all the time. Need to disconnect the wire the runs to the light at the alt and do some testing with a meter.
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Re: Stupid lgen light question
Not trying to hijack, and staying on topic - Is the light at full brightness, or dim? And should you ever be able to see the light when the system is functioning properly? (For instance, if there is a large drain on the system - Running extra lights etc).
- Big Dave
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Re: Stupid lgen light question
If everything is functioning correctly, the light should either be off or very very dim (only able to see it glow just a bit in the dark).
If you can see it during the day, it may be charging, but its not going to be charging anywhere near full capacity.
If you can see it during the day, it may be charging, but its not going to be charging anywhere near full capacity.
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Re: Stupid lgen light question
Sounds about right. I only noticed mine (a medium glow) last night with the headlights and 4 offroad lights all turned on.
The OP's sounds like a short. At any rate I'd be more apt to trust the voltmeter than the light itself...
The OP's sounds like a short. At any rate I'd be more apt to trust the voltmeter than the light itself...
- birddog1148
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Re: Stupid lgen light question
Well it seams like it started when I switched motors, Wich was a while ago. but I driven it in about 2 years. I just installed a voltmeter in the dash and it shows 12-15 volts. A meter on the alt showed 13.5 volts, so I am at a loss. Will look at the wireing going to the light.
- Lotrat
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Re: Stupid lgen light question
Here's some good info on the light and it's operation: http://www.vw-resource.com/alternator_wiring.html#alt
Necessity for the Alternator Warning Light
It is absolutely essential that the (D+) terminal on the alternator be connected to a functioning "Alt" warning light in the instrument cluster. If this light is missing or defective, the alternator will NOT charge the battery! See my hand-drawn wiring diagram above. Also see Speedy Jim's diagram, which is much better than mine!
The system is very simple, but it's absolutely critical that you get it right. The (D+) terminal on the alternator MUST connect to a functioning warning light in the instrument cluster. There should be just one wire (blue) from the (D+) connector on the alternator to the button on the bottom of the normal indicator light in the dash. The dash light is also wired from the (D+) (Blue) to ignition terminal #15 on the coil, which in turn is connected to the positive (+) post on the battery (Black). There is no ground wire on the light; the body of the bulb is connected to ground via the light holder (which also provides the ground connection for the other dash lights as well.) The three bulbs (ALT/OIL/TURN) all have a common connection in the socket which goes to ignition terminal #15 on the coil (which receives power from the (+) post on the battery by way of the ignition switch).
The alternator must get a feedback current through the "Alt" lamp in the instrument cluster so it can sense the battery voltage; it uses that as part of the alternator's internal circuitry needed to charge the battery. In other words, with the ignition on but engine off, the indicator light sees 12 volts from the battery (via ignition terminal #15 on the coil) and glows, but with the engine running, it sees 2 volts (14 volts minus 12 volts) running the other way, from the alternator. It doesn't glow (needing more than 2 volts to do that), but the alternator still "sees" the connection to the battery.
So -- If the Alternator is charging, the (D+) terminal has 12 volts on it; the blue wire from (D+) carries 14 volts to the "Alt" light in the instrument cluster. When the engine is running, there is 12 volts on the *other* side of the lamp from ignition terminal #15, so potential difference is only 2 volts and the bulb doesn't light. But, if the alternator dies or the drive belt breaks, there is no voltage on (D+) (looks like ground) and current flows from #15 thru the lamp to (D+), and the "Alt" lamp comes on to warn the driver of a problem.
An LED light won't work for this purpose. LED's are diodes and will not allow current to flow in the opposite direction. With the LED, it would see the 12 volts, but the reverse flow 2 volts would be stopped by the diode nature of the LED, so that wouldn't work.
The 12-volt 2-watt indicator bulbs are available at any VW parts store. The same bulb is used for the speedometer illumination bulbs (two of them) and the other indicator bulbs in the instrument cluster. In a pinch you can borrow one of the illumination bulbs to replace a blown Alt indicator bulb -- the speedometer will be a bit dim on one side but can still be seen until you get a replacement bulb.
Necessity for the Alternator Warning Light
It is absolutely essential that the (D+) terminal on the alternator be connected to a functioning "Alt" warning light in the instrument cluster. If this light is missing or defective, the alternator will NOT charge the battery! See my hand-drawn wiring diagram above. Also see Speedy Jim's diagram, which is much better than mine!
The system is very simple, but it's absolutely critical that you get it right. The (D+) terminal on the alternator MUST connect to a functioning warning light in the instrument cluster. There should be just one wire (blue) from the (D+) connector on the alternator to the button on the bottom of the normal indicator light in the dash. The dash light is also wired from the (D+) (Blue) to ignition terminal #15 on the coil, which in turn is connected to the positive (+) post on the battery (Black). There is no ground wire on the light; the body of the bulb is connected to ground via the light holder (which also provides the ground connection for the other dash lights as well.) The three bulbs (ALT/OIL/TURN) all have a common connection in the socket which goes to ignition terminal #15 on the coil (which receives power from the (+) post on the battery by way of the ignition switch).
The alternator must get a feedback current through the "Alt" lamp in the instrument cluster so it can sense the battery voltage; it uses that as part of the alternator's internal circuitry needed to charge the battery. In other words, with the ignition on but engine off, the indicator light sees 12 volts from the battery (via ignition terminal #15 on the coil) and glows, but with the engine running, it sees 2 volts (14 volts minus 12 volts) running the other way, from the alternator. It doesn't glow (needing more than 2 volts to do that), but the alternator still "sees" the connection to the battery.
So -- If the Alternator is charging, the (D+) terminal has 12 volts on it; the blue wire from (D+) carries 14 volts to the "Alt" light in the instrument cluster. When the engine is running, there is 12 volts on the *other* side of the lamp from ignition terminal #15, so potential difference is only 2 volts and the bulb doesn't light. But, if the alternator dies or the drive belt breaks, there is no voltage on (D+) (looks like ground) and current flows from #15 thru the lamp to (D+), and the "Alt" lamp comes on to warn the driver of a problem.
An LED light won't work for this purpose. LED's are diodes and will not allow current to flow in the opposite direction. With the LED, it would see the 12 volts, but the reverse flow 2 volts would be stopped by the diode nature of the LED, so that wouldn't work.
The 12-volt 2-watt indicator bulbs are available at any VW parts store. The same bulb is used for the speedometer illumination bulbs (two of them) and the other indicator bulbs in the instrument cluster. In a pinch you can borrow one of the illumination bulbs to replace a blown Alt indicator bulb -- the speedometer will be a bit dim on one side but can still be seen until you get a replacement bulb.
- birddog1148
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Re: Stupid lgen light question
Lotrat, I have that bastard externaly regulated alternator with 4 wires
- david58
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Re: Stupid lgen light question
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- fusername
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Re: Stupid lgen light question
Bet u pinched the blue one putting in the new motor, maybe even clean cut it, cause I feel like if the blue wire got grounded but twas still connected to the alt it probably wouldn't charge. I would, if you access easy enough, pull the two wires for the warning light. Check for continuity to ground on both of them, then key on engine off check for 12v on the non blue wire
Electrical is a jerk, but I am lucky enough to have a vague understanding of how it works so I kind of enjoy helping others diagnose. Now when it comes to tuning carbs, swing on by and do it for me eh?
Electrical is a jerk, but I am lucky enough to have a vague understanding of how it works so I kind of enjoy helping others diagnose. Now when it comes to tuning carbs, swing on by and do it for me eh?
give a man a watch and he'll allways know what time it is. give him two and he can never be sure again.
Things are rarely just crazy enough to work, but they're frequently just crazy enough to fail hilariously.
Things are rarely just crazy enough to work, but they're frequently just crazy enough to fail hilariously.
- fusername
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Re: Stupid lgen light question
Oh and a dim light, noticale at night is fairly common/on every vw. Mine gets brighter when the blinkers and such come on, due to old wiring in the dash, meaning anything that draws power on the dash causes it to get brighter. Has nothing to do with the state of the charging system but rather with voltage drop in the indicator lights
give a man a watch and he'll allways know what time it is. give him two and he can never be sure again.
Things are rarely just crazy enough to work, but they're frequently just crazy enough to fail hilariously.
Things are rarely just crazy enough to work, but they're frequently just crazy enough to fail hilariously.
- Turbo_Manx_Maniac
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Re: Stupid lgen light question
The light gets a 12 volt source from the ignition system, when the Alt is not turning it internally grounds D+ and current flows from the ignition source throught the light, through the Alt to ground and the light will illumunate.
When the Alt is turning fast enough to charge, it switches the D+ wire to +12V, now the Alt light has +12V on each side, with no difference in voltage potential the light cannot illuminate.
When it glows slightly, that means there is a difference in voltage across the light. This can be caused by weak wiring to the ignition source side of the Alt light providing ~12V at the ignition side, but 14V at the Alt side. A check with a Volt meter will tell you if the voltage on the ignition or Alt side fo the light is lower.
Another check is to use your voltmeter on AC, and measure the voltage from the Alternator B+ wire (The big one). Typically the Alt light goes on dimly because one of the diodes in the Alt has failed or is failing, you will still get 13-14V DC, but there will also be measurable AC on the B+ wire. Anything higher than a few volts AC means the Alt is failing.
A few simple checks should tell you what's going on.
I don't agree that it's normal for the ALt light to glow dimly, I've always been able to point to shoddy wiring or a bad Alt/Gen as the culprit. If you understand how the Alt light works you will understand there is a voltage drop somewhere that's making it illuminate.
When the Alt is turning fast enough to charge, it switches the D+ wire to +12V, now the Alt light has +12V on each side, with no difference in voltage potential the light cannot illuminate.
When it glows slightly, that means there is a difference in voltage across the light. This can be caused by weak wiring to the ignition source side of the Alt light providing ~12V at the ignition side, but 14V at the Alt side. A check with a Volt meter will tell you if the voltage on the ignition or Alt side fo the light is lower.
Another check is to use your voltmeter on AC, and measure the voltage from the Alternator B+ wire (The big one). Typically the Alt light goes on dimly because one of the diodes in the Alt has failed or is failing, you will still get 13-14V DC, but there will also be measurable AC on the B+ wire. Anything higher than a few volts AC means the Alt is failing.
A few simple checks should tell you what's going on.
I don't agree that it's normal for the ALt light to glow dimly, I've always been able to point to shoddy wiring or a bad Alt/Gen as the culprit. If you understand how the Alt light works you will understand there is a voltage drop somewhere that's making it illuminate.
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