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Date:         Sun, 29 Mar 2009 18:51:12 -0700
Reply-To:     David Kao <dtkao0205@YAHOO.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Kao <dtkao0205@YAHOO.COM>
Subject:      Re: 88 Vanagon alternator light problem
In-Reply-To:  <194423170903291650y31358a81n4ec45a46682ed76@mail.gmail.com>
Content-Type: text/plain; charset=us-ascii

Here is an easy diagnose procedure if the alternator light stays on. With the engine running (at idle) unplug the small connector on the back of the alternator. If the light goes off the circuitry of the alternator light is fine. It is the alternator that is not generating current.

That terminal for the small connector is internally driven by the output voltage of the alternator. If the alternator is generating current (and the correct voltage) it feeds that terminal with 13.8 volt, the present of this voltage will cause the alternator light to go off. If this voltage is not present (alternator not generating current) the light will come on. This is a simplified alternator light circuitry:

Battery 12V--->resistor--->bulb<---terminal (alternator voltage)

Well, this is just a simplified diagram. The alternator terminal is connected to the control field winding. It's a black box there. But basically if the alternator voltage is not present at that terminal the light will come on to tell you that the alternator is not generating current (voltage). You can measure the voltage at the terminal if you have a meter. With the ingnition key turned on but before cranking it should have a small amount of voltage only. Once the engine is started it should have 13.8 volt.

David

--- On Sun, 3/29/09, John Graham <theklube@GMAIL.COM> wrote:

> From: John Graham <theklube@GMAIL.COM> > Subject: 88 Vanagon alternator light problem > To: vanagon@GERRY.VANAGON.COM > Date: Sunday, March 29, 2009, 4:50 PM > Dear list, > > Well, I titled this 'alternator light problem' > because that's what happened > first. Here's what has happened so far. > > I was coming back from the campout at Hunting Island when I > noticed that my > alternator light was on! At first it was Oh Sh...t as I > was driving along a > two lane road with NO shoulder, but the temp guage was > right where it should > be and I had no other indications that anything was wrong. > I stopped for > gas several miles later and found no missing belts or loose > connections in > the engine compartment. AND there appeared to be no > reduction in battery > power when I restarted, so I'm thinking something other > than a gross failure > of the charging system. > > While I was sitting in the gas station pondering my > situation, the only > thing that I noticed that was further info was that when I > shifted the > automatic from park down to drive and back, the alternator > light flickered a > little. I tried clicking on the headlights and there was > no flicker at all > and the lights seemed to come on full. So with my tank > full of gas and only > 3 more hours of interstate travel to get me back home, I > set off. > > During my remaining trip, I noticed that the light would go > off for long > periods of time and then come back on. It stayed mostly on > during the > trip. I didn't try wiggling any of the instrument > panel connections, but it > occurred to me. > > I just went out and checked to see the specifics of details > as I moved that > auto trans lever. The light is on full bright in Park and > Neutral, but is > slighty dimmer in Reverse and the Drive settings > > Any ideas of where I might look next? > > Thanks, > > John Graham > 88 Westy > Charlotte, NC > > -- > This e-mail is a natural product made from recycled > electrons. The slight > variations in spelling and grammar enhance its individual > character and > beauty and in no way are to be considered flaws or defects.


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