Guess what's wrong (charging issues)

[92EcoDiesel Jetta]

My alternator light on the cluster has never worked. When engine starts, charging does not start immediately. It may take 5 to 15 minutes of driving before it starts to charge. The battery always gets charged and never let me down so it was not a high priority item to fix. Last week I decided to look into it and disconnected the excitation wire (blue wire) from the alternator to see if there was voltage on it. With the wire disconnected, I went to start the engine and it WOULD NOT START! That's not suppose to do that right? I didn't have the Bently with me so had to stop. Any guess as to what's mis-wired? I will be trouble shooting this again- Bently wiring diagram in hand.

[Quantum TD]

That should not happen. The main batter cables lead to the alternator and the starter, not in sequence. And, power to the starter is constant, while power to the solenoid comes thru the ignition switch.

A bad LED on the dash cluster may interrupt the charging circuit. I was told by my cousin back in the day, that the LED is a link in the system. Without it, charging will not occur. Needless to say, that may be hooey.

Anyways, it can't hurt to pull the alternator and have it tested at like Autozone for free. If it's bad, start there and then work to the LED on the cluster

[92EcoDiesel Jetta]

QTD. thanks for the ideas. I failed to mention that with blue excitation wire c onnected (which allowed cranking the starter motor), I started the engine then disconnected the blue wire. DVM indicated 12 V (not charging).. I then connected a test light betwwen battery + and excitation terminal of alternator and DVM immediately jumped to 14 volts.

I think the alternator is fine. It is not getting excitation voltage (from the blue wire) and there is something screwy with that wire which causes a no crank condition when disconnected from the alternator.

[92EcoDiesel Jetta]

Another piece of info. Don't know if it matters or not but this alternator does not have a W terminal. The red/blk W terminal  wire was grounded to the alternator from PO. I removed it from ground and it did not seem to make any difference.

[Rabbit on Roids]

probably just a gasser alt retrofitted on there. they bolt on the same.

[92EcoDiesel Jetta]

probably just a gasser alt retrofitted on there. they bolt on the same.

I dunno but it does not have a 2 terminal connector for the D+ and W connections as shown in the Bently wiring diagram but just a single screw terminal for D+.

Did some wire tracing today. Some idiot took the alternator blue excitatiom wire at the fuse relay panel and cut it from connector U2/12 and spliced it to the driver's seat belt switch wire at connector T2k/2 on current trace 95 (which is a ground wire, disconnected from ground 38). Anyway this ground also grounds the starting interlock relay. Ground was provided by the alternator excitation terminal, that's why when I disconnected the excitation wire from the alternator, the engine wouldn't crank. It was getting dark and I was disgusted at the prospect of more wire tracing and undoing what this idiot has done. More work to do.

[lovinthedeez]

I think the alternator is fine. It is not getting excitation voltage (from the blue wire) and there is something screwy with that wire which causes a no crank condition when disconnected from the alternator.

the alternator will "self excite" after about 2000 rpms.  the no crank situation has nothing to do with the exciter wire.  they break all the time and thats why the battery light usually stays on until you start driving.  the connection to the cluster is where it usually fails. 

[92EcoDiesel Jetta]

I think the alternator is fine. It is not getting excitation voltage (from the blue wire) and there is something screwy with that wire which causes a no crank condition when disconnected from the alternator.

the alternator will "self excite" after about 2000 rpms.  the no crank situation has nothing to do with the exciter wire.  they break all the time and thats why the battery light usually stays on until you start driving.  the connection to the cluster is where it usually fails. 

They indeed are separate issues. Just so happen the idiot who hacked into the wiring caused both problems to occur. All is well now. I spliced the blue excitation wire back onto connector U2/12 and grounded the wire to the starter lockout relay. The alternator light is working (for the first time) and it starts charging immediately upon engine start! I also added the missing glow plug LED (I have a Jetta gasser cluster with LCD clock and tach) by soldering in the missing 470 ohm current limiting resistor and wired up the LED. It's a green LED though, not yellow, because the cluster I stole the LED from was a gasser cluster and there is no yellow LED.

[RabbitJockey]

you can swap leds, i used a cabriolet cluster on my jetta mk1 and also had to solder in the extra resistor.  also does your tach jump all over the place?  or do you have it converted?  i had a similar charging problem on my girlfriends cabriolet which turned out to be a faulter instrument cluster membrane

[92EcoDiesel Jetta]

My tach does not jump. It is smooth and responsive. I converted it to run off 2 magnets on the crank pulley.