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Re: [Mgs] Alternator, battery, fan, or normal?

To: "Aaron Whiteman" <awhitema@panix.com>, <mgs@autox.team.net>
Subject: Re: [Mgs] Alternator, battery, fan, or normal?
From: "PaulHunt73" <paulhunt73@virginmedia.com>
Date: Fri, 21 Sep 2012 09:03:58 +0100
Delivered-to: mgs-archive@autox.team.net
Delivered-to: mgs@autox.team.net
References: <44DB0CEB-709A-48CA-8239-F82BEC0B5D7D@panix.com>
The light will glow if there is a potential difference between the white 
side of the warning light, which comes from the ignition switch, and the 
brown/yellow side which comes from the alternator indicator terminal.  In a 
good system it shouldn't glow.

It usually indicates the alternator is failing, possibly one or more of the 
diodes, but it will also happen if you have bad connections between the 
alternator output terminal, via the solenoid connection and ignition switch 
to the white circuit.  In both these cases it will glow brighter with 
increasing load.

Measure the voltage between the output (brown) and the indicator 
(brown/yellow) terminals on the alternator - wiring connected, engine 
running, electrical loads switched on, such that you have the glow.  If 
there is a potential difference between those two (other than perhaps a 
couple of tenths of a volt), then the alternator itself is the culprit.  If 
either of them are over 14.7v then again the alternator is the culprit.  If 
they are much the same but there is a potential difference between the 
output terminal and the ignition switch white such that the white is lower 
than the output terminal, then it is a bad connection between the two.

The heater fan and the overdrive come off the white circuit so the problem 
could either be in the brown or the ignition switch.  If the headlamps make 
no difference it will be the ignition switch circuit, if the headlamps make 
a difference then it will be in the brown circuit.  Exactly where it could 
be in either case depends on the year as wiring varies.

PaulH.

----- Original Message ----- 
>I noticed tonight that the red battery light has just a hint of red as I 
>was
> driving home.
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