# Blue exciter wire question



## DuncanDonutz (Nov 17, 2009)

So...my car died while I was driving a few days ago, narrowed it down to the alternator and replaced that. Unfortunately, I'm still only reading about 12.8 v at the battery even with the engine running at 2-3k RPMs. Well, I jumped on here to do some troubleshooting and noticed alot of threads related to the infamous blue exciter wire, and what I found troubled me. Now apparently the blue exciter wire is supposed to be routed through the warning lamp, but on my car it is plugged into a terminal on the starter solenoid. (This also explains why my alternator idiot light has never worked). It's been like this since I bought it 2 years ago, I'm not really a wiring guy so I never realized this was a problem. Now, from what I've read on here the blue exciter needs to be wired through a diode for it to work correctly. Could this be whats causing my charging problem? If so so why are the symptoms only evident now and never in the last two years? Any help would be greatly appreciated, thanks guys!


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## DuncanDonutz (Nov 17, 2009)

Well I went out to fiddle with it some more, and I think part of the problem is my crappy voltmeter. It read only 11.8 v across the battery terminals but she fired up just fine, so clearly it's way off. Drove her around for 15 mins or so, and when I parked her the voltmeter read 12.2 v across the terminals. Gonna drive her to work and school tomorrow and hope I dont run into any problems!


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## WaterWheels (Aug 14, 2005)

Your battery reading when using that volt meter does not really indicate it is bad (the volt meter). You can do some simple tests using other things like a fresh 9v battery or 110v wall outlet or a different car battery to see if the reading seems OK. That you received a higher reading after driving the car a little indicates that at least some charging is taking place even if only a little. And 11 volts unless it is really cold and the car sat for a while should be enough to crank it over if the rest is in tune.

OK, you replaced the alternator, but they are much too often bad when you buy them as not many places do quality rebuilds anymore. Not saying yours is no good, just that replacing one with a rebuild is no sure fix if the old one was in fact the problem. Just where and how have you been doing the voltage testing? Have you tested directly off the alternator? Tested using different ground locations, like the battery, the chassis and the alternator housing? What I’m getting at is that often testing is done wrong or multiple test locations are not used to narrow down a fault. Testing always between the battery + and – never takes the wiring into account for example.

The location that some _ _ _ _ _ (fill in the blanks) used to connect the exciter wire was a problem. The general route for an exciter circuit is power from either battery or ignition – through LED dash light (often with resistors in the circuit in case the light burns out) – to the alternator D+ connection. It can, as with Volkswagens, run through the relay panel to aid in wiring the car. Which end of the exciter circuit was plugged on to the starter? One way could cause the light to stay on and allow no charging to take place and the other way would only excite the field when the engine is being cranked and then stop when the key is released. That I believe would also cause a no charge situation (not really sure but I doubt the alternator is spinning fast enough to maintain charging while only cranking?), cause the “BATT” light to maybe just kind of flicker or stay on only while cranking and possibly damage the diode trio in the alternator (just a guess). I suggest you do a fast Google on the charging system and exciter circuit as that should net you tons of information on how it works and troubleshooting. Why this problem just now showed up after two years of being connected that way is a bit of a puzzle to me.


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## L33t A2 (Aug 5, 2003)

*FV-QR*

http://forums.vwvortex.com/showthread.php?5469825-Blue-exciter-wire...again....


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## ziddey (Apr 16, 2006)

It is theoretically possible to excite the alternator via the starter terminals. In reality, the rpm is usually too low. You read about people needing to blip up to just under 2k before the alternator excites frequently (of course you can fault that to worn brushes or bad grounds).

I've gone without an instrument cluster before. I ran a temporary wire from the d+ to the battery area, and would pop the hood and tap it on the battery+ every time I started the car. Once excited, the alternator will stay excited. You'll be able to hear it, as well as the extra load now on the engine.

The diode is to prevent battery drain while the car is off I believe.

I'm not really that knowledgeable on the charging system in terms of how the regulator functions, and if not having d+ attached after initial excitation would allow the possibility of overcharging, although I doubt it, especially since it's pretty similar to your current d+ to starter method.


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## filthyillness (Feb 13, 2010)

I'm gonna add on into this. I just installed the Innovative Wiring Ground Kit. It's a pretty nice kit. Anyways, the field wire (blue exciter wire) came with an OEM connector that is supposed to attach to the harness where the field wire originates from. My blue wire strings along into the rest of the wiring harness, no connector. It was originally one straight shot from inside the car, from the fire wall, to the alternator. It worked when I first picked it up, but got messed up from rubbing against the transmission.

Now, my thing is if so many people know about this and know how to fix it. Can someone post a pic of how the bays looks with the field wire, from the harness, and how it connects to the alternator. Thanks!


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## filthyillness (Feb 13, 2010)

BUMP. Someone post a pic of how the field wire attache's to the rest of the engine wiring harness and where.


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