Alternator woes

Hey guys, I'm having a charging system problem that I hope you guys can help me out with.
Now, I know the charging system is simple enough in my 1986 GTI that I
shouldn't need a lot of help, but, well, whatever.
My car has ceased to charge itself. The battery and its related cabling, fusible links, etc are all fine, as indicated by the fact that if the battery is charged externally (by trickle charger or jumper cables) the car runs just fine, until the battery runs down and the car dies. So I picked up an alternator from Advance Auto, swapped it in, and I still have no charging effect.
Now, I have a couple issues with the new alternator that bother me.
First, the old alternator has a small plastic box screwed to the back, with a black wire connecting it to a spade terminal on the alternator marked +. The plastic box is marked with a bunch of stuff, including a line reading "2.2uF 100V", indicating it's a smoothing capacitor of some sort. The new alternator does not have this piece. If it's just a smoothing cap, is this critical? i.e. would lacking this part cause the new alternator not to charge my battery? If it is critical, does this part have a name? I have not seen it referenced anywhere, in the Bentley manual or on the web. Should my new alternator have come with it?
Second, the old alternator had the blue wire for the idiot light connected to a spade terminal labelled D. The new alternator has an empty hole marked D with no spade terminal, and a different hole marked W that _does_ have a spade terminal. What gives? Am I supposed to hook up the blue wire to the W terminal now? I suspect not... Regardless, seeing as how it's just for the idiot lights, I left it unconnected until I can verify how it needs to be hooked up.
So basically, I now have the new alternator in the car with only the red wire from the starter cable connected to it, and it grounds through the engine. Ive done a little checking with a voltmeter, and I've got good clean continuity from the Battery + to the alternator B+ (through the starter), and good clean continuity from the Battery - to the alternator housing. Still no charging effect, and I'm not sure where to look next.
Sorry for the long-winded question, thank you all in advance for any assistance you might provide.
Mike
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Mike wrote:
<snip>

I haven't looked at my '87 alternator lately, but I know the voltage regulator is replaceable. It almost seems like your new alternator came without a voltage regulator. Do you still have the old alternator?

The blue wire goes to the idiot light, but its presence is absolutely critical to the charging system. Alternators can not deliverer any power unless the field winding is energized, and the field winding does not get energized unless the alternator is delivering power. To overcome this, if the alternator is not delivering enough power to energize the field winding, the current that goes through the idiot light and the blue wire is used to energize the field winding until the alternator starts putting out current. So, disconnected blue wire = no power from alternator. Again, it seems like your new alternator has a dummy plate put in in place of the voltage regulator.
The W terminal is used for the tachometer on diesel engines. Since there is no ignition system on diesels, is was common to take a signal from the alternator, before the diodes, to run the tachometer. These days, they probably use crank sensors like on a gas engine.
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Magically delicious!

This turned out to be the culprit. I didn't have it hooked up to begin with because the hole marked D where the blue wire should've hooked up to was empty, there was no spade terminal to clip the wire to. Well, upon what had to be my 12th inspection, I noticed that the new alternator had a second large cable connector (as in, threaded stud with a nut just like the stud for the starter cable) that i had previously been ignoring. This large stud is marked D+, and had a tiny spade terminal sticking out of the back side of it where I hadn't noticed before. Hooked it up, jumped it, and it works beautifully.
Thank you very much, Randolph!
Mike
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Mike, that little plastic box is the rectifier/voltage regulator, I believe, and without it, your alternator doesn't make DC current, which is what your car needs to run. Swap in the old one off your old alternator, or buy a new one, they're not real expensive.
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Mike wrote:

If the new alternator does not have the "D" terminal you are screwed, that terminal is the excitation for the regulator. Someone screwed up in the alternator factory. THat's why the new one is not charging. I believe the "W" terminal is a connection for a tachometer for Diesels.
Do you still have the old one? Unless the bearings are going, a new regulator is 90% of the time all you need.
good luck,
nate
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