The warning lamp acts as a pump-primer to the alt. IME used alts will still
charge with the lamp disconnected, but only after being revved to 3k or so
(after that they will charge as normal down to about 600 rpm). However new
alts may not be able to do this which is why the warning light is so
important.
If you have 12v at the battery and 14v at the alt then there is a break in
the brown(s) between the two - it is nothing to do with the lamp.
The two browns are in parallel - on certain eras of car/alt the voltage
sensing was done remotely where the alt connects to the heavy current cable,
later alts do the sensing inside the alt and hence only need one (thick)
brown. When charging all three (in your case) wires should be at, or very
near, the same voltage. When not charging the browns should carry battery
voltage and the brown/yellow should show a near-ground.
PaulH.
----- Original Message -----
From: Scott Allen <scottinarl@hotmail.com>
To: <mgs@autox.team.net>
Sent: Sunday, October 07, 2001 4:19 AM
Subject: Last question
> I'm going to replace my voltmeter tomorrow so I can test each component in
> the charging system. Looking at John Twists's book, he says that I should
> get 14+ volts at the battery and at the back of the alternator.
>
> So, to test out my theory about the warning bulb being the culprit, I
figure
> that if I put the voltmeter on the battery it should show 12 volts or
maybe
> a bit less, (since it's not being charged). If I put it on the alternator
> it should show 14+, ergo it's somthing in between, (like the bulb) that's
> keeping the battery from charging.
>
> Here's my question: John Twist's book does not say which wire on the back
of
> the alternator to test. My choices are fat brown, thin brown, and thin
> brown/yellow. Could anybody on the list that's done this let me know?
///
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