blue alternator wire/battery light/no voltage

[theonlyred16v@hotmail.com (Brian Haygood)]

Blue wire runs from battery (+), through instrument panel/warning light, and 
on to the alt.  It brings +12v to the alt.  The current from this wire is 
used to get the alt going, called "exciting" the circuit.  Without an 
initial current like this the alt will never get going.  It's a good bit 
like priming a pump.

The circuit at the instrument panel compares the voltage on the two ends of 
the wire as well.  If the alt voltage is not slightly higher than the bat 
voltage, then the light comes on to tell you it isn't charging.

BH

>From: Vince Royer <vince@performancecarstereo.com>
>Reply-To: vince@performancecarstereo.com
>To: Brian Haygood <theonlyred16v@hotmail.com>, rocco2nr@hotmail.com, 
>scirocco-l@scirocco.org
>Subject: RE: blue alternator wire/battery light/no voltage
>Date: Thu, 10 Oct 2002 01:32:00 -0700
>
>So does the blue wire go from the alt to the insrument panel or does it go
>to the battery?  does the alternator send 12v down the blue wire, or does 
>it
>need to see 12 volts from the blue wire to work?
>
>What if my blue wire is hanging unused because I thought it was only for 
>the
>alternator light?  (Thus I haven't hooked it up to anything yet)
>
>Vince
>
>
>
>-----Original Message-----
>From: scirocco-l-admin@scirocco.org
>[mailto:scirocco-l-admin@scirocco.org]On Behalf Of Brian Haygood
>Sent: October 9, 2002 10:44 PM
>To: rocco2nr@hotmail.com; scirocco-l@scirocco.org
>Subject: Re: blue alternator wire/battery light/no voltage
>
>
>I'm going through a little blue-wire thing myself.  Here are my tips:
>
>Measure voltage between back of alt (big positive terminal nut) to alt 
>body,
>first with car off, then with it on.  If voltage is lower when on, alt is
>not charging, but...
>
>Run a wire from +12 terminal of battery to end of blue wire on alt.  
>Voltage
>probably won't change until you rev the engine.  If your alt raises the
>measured voltage when you rev it a little, your alt is good to go.  I have
>to rev mine to ~3 grand at times for some reason.
>
>If that does work, you have blue-wire blues of some form. With engine not
>running, but ignition on (don't know about ignition off) you should see 
>+12v
>at the end of the blue wire.  If not, check the connection at the positive
>battery terminal.  If still no, check it at the instrument panel.  That's
>all I know.
>
>My alt needs the afore mentioned high revs to get excited, and my blue 
>light
>doesn't work at all, though my blue-wire is consistently getting the needed
>+12.  Not a very good combination. I'm still working on that.
>
>BH
>
>
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