Technical Electrical Question due to a possible Mistake

[AndyBees]

The 2002 ALH engine in my Vanagon needed a new Glow Plug Harness. It was throwing DTCs as well as being all brittle and falling apart. It is a 4-wire GP Harness with a long pig-tail having a 4-Pin Connector.

So, here is the stupid mistake I made. I crawled under the Van out in the drive-way and proceeded to find a 4-Pin Connector. Wow! I found one. I promptly unplugged and plugged in the new GP Harness.

Damn. Why did VW make two different sets of circuits that have Connectors that can be plugged together? The long pigtail should have prompted me to question what I was about to do. Yes, I should have spliced-in the GP Harness at the engine and been done with it.

So, I mistakenly plugged the GP Harness to the connector that contains the DFM circuit from the T121/38 pin at the ECU to the Alternator and the L circuit that's connected to the Cluster at T32/12 (battery light) as well as the AC Positive for the coil from the On switch (Temp Control dial of the Vanagon AC system) and Ground for the AC coil.

Those circuits would have been Connected to the Glow Plugs. (Don't confuse this to mean the above got voltage from the GP relay.)

In the Connector

#1 - goes to the DFM circuit on the Alternator from the ECU at T121/38. This circuit allows the ECU to monitor Alternator output which is utilized to maintain engine speed as more current is drawn when things are turned On such as lights, AC, radio, wipers, signal lights, brake lights, tail lights, etc.
#2 - goes to the Alternator at L which is from the Cluster at T32/12 for the Battery Light Symbol
#3 - goes to the AC Coil for Positive
#4 - goes to the AC Coil for a Ground

So, now, with everything plugged correctly, the Battery Light Goes out when the engine is started, but the ALT doesn't seem to be charging. VCDS shows 11.55 Volts with the engine idling. Adding a 12 Volt Charger set on 2amps will only raise the voltage up to 11.63.

The engine starts fine. The accelerator is responsive. The only DTCs are the codes for the 4-GPs because the harness was cut-off at the engine.

The Alternator and AC Compressor could not have been damaged because they were obviously unplugged.

The only thing I can see that may be "screwed" is the ECU, circuit #1 in the above. But, since Circuit #1 is a signal (150Hz) to the ECU, a Glow Plug couldn't send such a signal.

Thoughts!

 

[AndyBees]

Well, I think I've solved the mystery.

A few days ago, I started the TDI Vanagon and turned on the AC in 88F ambient temp to see how long it would take for the Compressor to cycle off as well as at what Temp for the setting. After about 15 or 20 minutes, I had to leave my tinkering and attend to another matter totally unrelated. Before I turned off the engine, I noticed the digital dash mounted Volt Gauge was flashing at something below 12 volts (some LEDs are burned out, so it was difficult to read). Anyway, I forgot about the flashing gauge which indicates low voltage.

Then, today, when I first started the engine, I was seeing the same flashing low voltage from the gauge which I obviously never gave it any thought.

Anyway, trying to find the problem, I disconnected the B1+ positive cable on the Alternator and checked voltage with the engine idling....... 1.7 Volts.

Obviously this was a coincident because as I described in the opening post to this Thread, the DFM circuit is the only thing that could have been affected which I really don't see that happening considering it was connected to a Glow Plug that had no current on it, zero.

Well, I suppose I've learned a bit with this incident. Don't trust what would be logical when it comes to connectors being or not being interchangeable as far as fitting together.

EDIT: But, will 1.75 volts be enough to turn-off the Battery Light in the Cluster? Hmm.

 

[AndyBees]

Follow-up.

Yesterday, I pulled the Alternator and installed a new Bosch Brush/Regulator set. The only improvement was something over 2 volts.

So, today, I installed a new Alternator straight of out of the box. Now, I'm getting slightly under 5.5 volts. The only DTCs are for Glow Plugs because I cut the old harness off at the engine and have not installed the new one. This is what got me to this point, I think.

Does anyone have a clue what's going on? Read my first two posts to this Thread for a detailed reference.

@burpod

 

[AndyBees]

I suppose this is final update.

Okay, I checked the continuity of the L wire (exciter and battery light in the cluster) and the DFM wire (refer to post #1 for explanation of purpose). They checked out just fine. And, there was voltage on the L wire at the Alternator.

But, with the engine off, there was no voltage at the B+ on the Alternator (which is a direct connection to the Battery).
So, with everything connected properly, I checked voltage at the B+ with the engine idling --- wow, 13.67 to 13.73 volts. However, at the Battery, the voltage was under 12.4 volts.

Flash back to last summer/fall, I did a lot of work to the Van (wiring, AC system, clutter reduction with wires, etc.). As part of the clutter reduction, I wanted to eliminate as many wires from the Positive Post at the Starter as possible. I installed a bus bar using an old Briggs and Stratton Starter Relay. Like all similar relays, it has the two posts on top. I bridged the two posts using a piece of Aluminum. I connected the big B+ Alternator wire to one of the posts, a wire for the typical power to the dash of the Van, battery wires, etc.

Anyway, a few days ago, I ran the AC for at least an hour, head lights on, flashers, etc., making sure everything was working properly. So, I suspect there is a very bad connection between the Aluminum an Copper there on the improvised Bus Bar that I made.

I'll get back to it Monday.