That was way back when people cared and had pride about their work
Electrical puzzler...
- Thread starter DorianL
- Start date
Ira, did you ever put a test light to the D+ spade terminal of the alt and the other wire to the chassis? If the light stays on you have a diode with an internal short.
You do have a 71 alt right? 72 and 73 have external regulators, 71's have internal regulators.
When you turn the key to "on" you should have only the alt/gen and the oil lights on, nothing else. If the turn signal light comes on wires are crossed under the dash which is common on restorations. There is only 2 wires coming from the alt, one large, one small. The small wire runs up front to the headlight switch and off to the idiot light.
I would connect a temp but separate idiot light and see how that behaves.
I would connect a temp but separate idiot light and see how that behaves.
Clever
I think this is an internal regulator... years always confuse me.
Will do that as well. Damn, so that's that those screwdriver light probes are for
Yes both my idiot light come on bright when stalled and go off when the engine is running. Tho' Alt idiot light is intermittent.
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!
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.
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.
That and the fact that as I mentioned above about LED lights won't work because, well it's all written above.Will do that as well. Damn, so that's that those screwdriver light probes are for
Fantastic write up thanks! And that explains quite a few things! The idiot light I am using is not a LED or have a diode in it. I'll check my wiring and do all the tests you mention. I'll just add that for a long while, this actually did work. This idiot light beginning to glow is a very recent thing.
I am going to have to go through my wiring diagrams - again, mine is a GM harness with blade fuses adapted to the KG + I have an MSD Al6... I am VERY sure I don't have it wired going back to coil terminal #15.
Also I have an alternator with an internal regulator.
Also I have an alternator with an internal regulator.
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I wrote myself into a corner. I need a 36mm socket to remove the fan to get the alt out. Turns out I leant mine to a buddy... so I'm stuck.
That being said, I got a closer look at the alt installed on the engine: made in Brazil. I thought I paid for a German unit.
In the meantime I picked up a used German unit that is known to work.
That being said, I got a closer look at the alt installed on the engine: made in Brazil.
I thought I paid for a German unit.In the meantime I picked up a used German unit that is known to work.
Are you sure you needed that alt replaced? Was the voltage drop under usage too close to the static charge or even less?
Did you pull up the cover on the alt and inspect the brushes yet?
Did you pull up the cover on the alt and inspect the brushes yet?
Well I guess we'll all know soon. Go by a repair shop and offer a comfortable deposit against a loan of the socket.
It was... intermittently
Oh? I thought the brushes were on the other side!
Does this.... look ok to you? If not... salvegable? Or neglible damage.
Richard you might have called it. Looking up how to inspect brushes, I found someone describing exactly the issue I'm having with intermittent problems with voltage drop.
Note the filament
Richard you might have called it. Looking up how to inspect brushes, I found someone describing exactly the issue I'm having with intermittent problems with voltage drop.
Note the filament