How alternator light works, a more detailed description Options

[Superhawk996]

Excited

Still having an issue, but seems as though the alternator comes into charging earlier. I am still unable to get the GEN light to light under any condition (Lamp will light with 12v applied). Red/white wire has switched battery voltage. Blue wire I cannot get anything, no voltage, no continuity to ground, nothing.

But, it seems as the system comes online quicker. Alternator was bench tested and was working according to my local rebuilder. Hate to source a new alternator, but kinda looking that might be the answer.

Do not put a new alternator into it until you’ve measured everything with a DMM with engine running.

When you say blue wire has nothing on it is that with engine running?

If that answer is yes, you need to trace continuity of the blue wire back to the alternator and where it is connected to on the alternator.

You also need to determine what wattage bulb you have for the generator light. When the change was made to internal regulators that bulb changes, too much resistance through that bulb limits alternator field excitation at start up.

I haven’t seen anything posted that would indicate you need a new alternator.

@930cabman

[Spoke]

Excited

Still having an issue, but seems as though the alternator comes into charging earlier. I am still unable to get the GEN light to light under any condition (Lamp will light with 12v applied). Red/white wire has switched battery voltage. Blue wire I cannot get anything, no voltage, no continuity to ground, nothing.

But, it seems as the system comes online quicker. Alternator was bench tested and was working according to my local rebuilder. Hate to source a new alternator, but kinda looking that might be the answer.

Test the GEN light with ignition ON but engine not running. First pull out the instrument with the GEN light so both terminals are accessible.

With ignition ON engine not running, measure the voltage to chassis on both sides of the GEN light.

Then measure the blue wire coming out of the alternator. It too should be equal to one of the GEN light spades.

Is the alternator bootstrapping earlier or do you just have the magic decoder ring (ie, blip the throttle) to get the alternator going?

[930cabman]

Excited

Still having an issue, but seems as though the alternator comes into charging earlier. I am still unable to get the GEN light to light under any condition (Lamp will light with 12v applied). Red/white wire has switched battery voltage. Blue wire I cannot get anything, no voltage, no continuity to ground, nothing.

But, it seems as the system comes online quicker. Alternator was bench tested and was working according to my local rebuilder. Hate to source a new alternator, but kinda looking that might be the answer.

Test the GEN light with ignition ON but engine not running. First pull out the instrument with the GEN light so both terminals are accessible.

With ignition ON engine not running, measure the voltage to chassis on both sides of the GEN light. 12V with the red/white wire 0V with the light blue wire

Then measure the blue wire coming out of the alternator. It too should be equal to one of the GEN light spades. Blue wire reads 0V, engine off or engine running

Is the alternator bootstrapping earlier or do you just have the magic decoder ring (ie, blip the throttle) to get the alternator going? The decoder ring seems to be working fine, after a couple blips, she comes right online putting out about 14 or so volts. maybe I leave well enough alone

[930cabman]

Excited

Still having an issue, but seems as though the alternator comes into charging earlier. I am still unable to get the GEN light to light under any condition (Lamp will light with 12v applied). Red/white wire has switched battery voltage. Blue wire I cannot get anything, no voltage, no continuity to ground, nothing.

But, it seems as the system comes online quicker. Alternator was bench tested and was working according to my local rebuilder. Hate to source a new alternator, but kinda looking that might be the answer.

Do not put a new alternator into it until you’ve measured everything with a DMM with engine running.

When you say blue wire has nothing on it is that with engine running? Yes, engine running

If that answer is yes, you need to trace continuity of the blue wire back to the alternator and where it is connected to on the alternator. A PITA with carbs, shroud, ...

You also need to determine what wattage bulb you have for the generator light. Stock wattage as far as I can tell. It will light with 12V applied. When the change was made to internal regulators that bulb changes, too much resistance through that bulb limits alternator field excitation at start up. So, an alternator will use a different bulb?

I haven’t seen anything posted that would indicate you need a new alternator.

Maybe I will continue to use the decoder ring (IMG:style_emoticons/default/aktion035.gif)

@930cabman

[Superhawk996]

When you say blue wire has nothing on it is that with engine running? Yes, engine running

If that answer is yes, you need to trace continuity of the blue wire back to the alternator and where it is connected to on the alternator. A PITA with carbs, shroud, ...

You also need to determine what wattage bulb you have for the generator light. Stock wattage as far as I can tell. It will light with 12V applied. When the change was made to internal regulators that bulb changes, too much resistance through that bulb limits alternator field excitation at start up. So, an alternator will use a different bulb?

I haven’t seen anything posted that would indicate you need a new alternator.

Maybe I will continue to use the decoder ring (IMG:style_emoticons/default/aktion035.gif)

@930cabman

Can’t help you if you choose not to troubleshoot the blue D+ wire. That wire should have a ground on it at start up and then goes to 12v once the alternator has been excited.

With respect to a bulb change. Seems crazy but if that charge lamp bulb doesn’t flow enough current - there is no excitation. See Porsche bulletin below

[930cabman]

When you say blue wire has nothing on it is that with engine running? Yes, engine running

If that answer is yes, you need to trace continuity of the blue wire back to the alternator and where it is connected to on the alternator. A PITA with carbs, shroud, ...

You also need to determine what wattage bulb you have for the generator light. Stock wattage as far as I can tell. It will light with 12V applied. When the change was made to internal regulators that bulb changes, too much resistance through that bulb limits alternator field excitation at start up. So, an alternator will use a different bulb?

I haven’t seen anything posted that would indicate you need a new alternator.

Maybe I will continue to use the decoder ring (IMG:style_emoticons/default/aktion035.gif)

@930cabman

Can’t help you if you don’t chase the blue D+ wire. That wire should have a ground on it at start up and then goes to 12v once the alternator has been excited.

With respect to a bulb change. Seems crazy but if that charge lamp bulb doesn’t flow enough current - there is no excitation. See Porsche bulletin below

How do you find this stuff?? I look and look and you guys find it. Thanks

maybe the bulb wattage is not allowing the alternator to get excited? sounds crazy, but leave it to those Germans (IMG:style_emoticons/default/idea.gif)

[Superhawk996]

maybe the bulb wattage is not allowing the alternator to get excited? sounds crazy, but leave it to those Germans (IMG:style_emoticons/default/idea.gif)

I highly doubt that. You could certainly try a higher wattage bulb (4W); won’t hurt anything.

As it stands right now you have 12v at key on on the red/white wire side of the bulb.

You state the current charge lamp bulb lights when tested separately so the bulb is OK

What is missing is a ground path on the blue wire when the engine is not running. You’ve said you checked blue wire and it has no path to ground, nor does it have 12v on the blue wire when running. Therefore, something isn’t right in the blue wire D+ (61) circuit.

The problem isn’t the bulb wattage at this point.

[930cabman]

maybe the bulb wattage is not allowing the alternator to get excited? sounds crazy, but leave it to those Germans (IMG:style_emoticons/default/idea.gif)

I highly doubt that.

As it stands right now you have 12v at key on on the red/white wire side of the bulb.

You state the bulb lights when tested separately so the bulb is OK

What is missing is a ground path on the blue wire when the engine is not running. You’ve said you checked blue wire and it has no path to ground, nor does it have 12v on the blue wire when running. Therefore, something isn’t right in the blue wire D+ (61) circuit.

The problem isn’t the bulb wattage at this point.

Perhaps a weak diode, if there is such a thing?

After a few blips she starts charging and stays charging until shut off. After a restart, a few blips are required to get her charging once again

[Superhawk996]

After a few blips she starts charging and stays charging until shut off. After a restart, a few blips are required to get her charging once again

That will work . . . until it doesn’t.

You are depending on residual magnetism in the armature to get the alternator excitation that isn’t being delivered to the field windings by the charge lamp circuit.

Proceed with caution.

[930cabman]

Got it, mostly. As you can imagine this has been driving me crazy and today I worked backwards from the lt blue wire on the GEN light. I was not finding continuity from the GEN light to the socket on the relay board, but I was getting about 100 ohms from the D+ wire to ground at the alternator. I had the D+ wire from the alternator plugged into the wrong socket on the relay board. I found the correct socket with continuity and now the GEN light comes on when the key is on, engine off. When the engine starts the GEN light stays on for a couple seconds, then goes out and a voltmeter indicates 14V +/-

Another bridge crossed with this /6 conversion.

BTW, she sounds great

[Superhawk996]

Got it, mostly. As you can imagine this has been driving me crazy and today I worked backwards from the lt blue wire on the GEN light. I was not finding continuity from the GEN light to the socket on the relay board, but I was getting about 100 ohms from the D+ wire to ground at the alternator. I had the D+ wire from the alternator plugged into the wrong socket on the relay board. I found the correct socket with continuity and now the GEN light comes on when the key is on, engine off. When the engine starts the GEN light stays on for a couple seconds, then goes out and a voltmeter indicates 14V +/-

Another bridge crossed with this /6 conversion.

BTW, she sounds great

Good job. Good finds. (IMG:style_emoticons/default/smilie_pokal.gif)

So this is where the bulb comes into play a higher wattage bulb will allow for higher excitation current and may turn off the light faster depending on what wattage is in there currently. 4 Watt is what the bulletin was trying to achieve.

[930cabman]

Got it, mostly. As you can imagine this has been driving me crazy and today I worked backwards from the lt blue wire on the GEN light. I was not finding continuity from the GEN light to the socket on the relay board, but I was getting about 100 ohms from the D+ wire to ground at the alternator. I had the D+ wire from the alternator plugged into the wrong socket on the relay board. I found the correct socket with continuity and now the GEN light comes on when the key is on, engine off. When the engine starts the GEN light stays on for a couple seconds, then goes out and a voltmeter indicates 14V +/-

Another bridge crossed with this /6 conversion.

BTW, she sounds great

Good job. Good finds. (IMG:style_emoticons/default/smilie_pokal.gif)

So this is where the bulb comes into play a higher wattage bulb will allow for higher excitation current and may turn off the light faster depending on what wattage is in there currently. 4 Watt is what the bulletin was trying to achieve.

Thank you, I was able to sneak away for a bit today and was determined, especially when my local rebuilder bench tested and gave it a thumbs up.

I am good with a couple second delay before the GEN light goes out and it could need a different wattage bulb

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