[V8] blue wire

[dsaad at icehouse.net]

Let me add a little more to this:

Does the alternator light come on when you first turn on the key? (motor not
running)
Does it go out when the motor starts?
If so then the light bulb is good, and the alternator is probably working.
If the above is true then measure the voltage at the battery posts and at the
alternator posts. If the voltage at the battery posts is below 13.8v but the
voltage at the alternator posts is at or above 13.8v then you may have a bad
battery cable connection or bad cable.

The reason the idiot light is off may have to do with where the alternator
"senses" the voltage. As far as it knows, everything is fine, but the voltage
drop from the alternator to the battery prevents the battery from charging.

Dave



Quoting dsaad at icehouse.net:

> I don't have my wiring diagrams handy - but I am 98.76% sure that this blue
> wire
> is the "turn on" wire. If you have 12 volts on it with the key on then it is
> probably working fine. I don't see the need to tear up the dash for this.
> I don't want to second guess your mechanic but - well really I do want to
> second
> guess him.
> There is likely to be a fuse for the alternator. Has he checked for it?
> Has he pulled the alternator and bench tested it?
> $80 an hour is too much to pay someone to learn how alternators work.
>
>
> Alternators 101:
> (this applies to almost any modern alternator with an internal regulator)
>
> The big heavy wire goes directly to the battery and is how the alternator
> charges the battery and powers the cars electrical system. It is the "output"
> of
> the alternator
>
> The smaller wire (usually marked "Field") has two purposes:
>
> First it supplies power (input) to the voltage regulator. When the key is in
> the
> "on" position you should see battery voltage on this wire.
>
> Second, it is the "voltage sense" wire. When the motor is running and the
> alternator is working, the alternator will keep the voltage on this input
> below
> around 13.8 volts. The regulator handles this job so if you have battery
> voltage
> on the blue wire and the alternator is not charging then you have a bad
> alternator.
>
> If there is a third wire it is usually for the idiot light or guage.
>
> There may also be a heavy ground wire.
>
>
>
> Dave
>
>
> Quoting Steve Kramer <skramer at mac.com>:
>
> > Fellow V8er's,
> >
> >     Last told you about my v8 not holding charge.  Mechanic says battery
> > light (alternator) does not go on. Can anyone lead me to the place where
> the
> > blue wire goes from the alternator to the instument cluster?
> >
> > He has the whole cluster taken apart and this is when that $80 bucks an
> hour
> > gets pretty scary.  Unfortunately, I cannot do this myself so I am at the
> > mercy of a mechanic who has very limited experience with a V8. :-(
> >
> >
> >
> > Thanks,
> >
> > Steve Kramer
> > 1990v8
> >
> >
> >
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>
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> contributions welcome!
>