Alternator replacement -- problem - Ford Forums - Mustang Forum, Ford Trucks, Ford Focus and Ford Cars

07-28-2005, 22:01

My car died (alternator has been weakening..now crapped out earlier
today) & I replaced the alternator. I jump started the car after I
replaced the alternator & it fired right up. The voltage level
(according to the car gauge) was dead in the center of the "R" in
"NORMAL" on the gauge.. normally it's on the "N" or "O".

The problem is... the battery symbol (MIL) is illuminated (red). It is
not going away at all. I tried disconnecting the battery ground cable
for 25 mins to reset the computer, but this didn't work. It holds a
good charge, but the light will not go away. I checked all fuses & none
are blown. Any thoughts?

Car is a 1998 Ford Mustang GT.

Thanks!!!!!!

-Mike

07-29-2005, 04:01

On Thu, 28 Jul 2005 21:06:38 -0700, memset@cellulean.com rearranged some
electrons to form:

> My car died (alternator has been weakening..now crapped out earlier
> today) & I replaced the alternator. I jump started the car after I
> replaced the alternator & it fired right up. The voltage level
> (according to the car gauge) was dead in the center of the "R" in
> "NORMAL" on the gauge.. normally it's on the "N" or "O".
>
> The problem is... the battery symbol (MIL) is illuminated (red). It is
> not going away at all. I tried disconnecting the battery ground cable
> for 25 mins to reset the computer, but this didn't work. It holds a
> good charge, but the light will not go away. I checked all fuses & none
> are blown. Any thoughts?
>
> Car is a 1998 Ford Mustang GT.
>
> Thanks!!!!!!
>
> -Mike

What is the voltage output of the new alternator? Are you
sure it's charging?

--
David M (dmacchiarolo)
http://home.triad.rr.com/redsled
T/S 53
sled351 Linux 2.4.18-14 has been up 7:36 1 user

07-29-2005, 04:01

I don't have a multimeter anymore.. can't find mine. It's def. "better"
than before though. I'm pretty positive it's charging.

-Mike

07-29-2005, 14:01

On 29 Jul 2005 03:43:52 -0700, "memset@cellulean.com"
<memset@cellulean.com> wrote:

>I don't have a multimeter anymore.. can't find mine. It's def. "better"
>than before though. I'm pretty positive it's charging.
>
>-Mike

A inexpensive thing to do would be to run down to the local Radio
Shack and pick up a $5-$10 DMM (digital multi meter). It's hard to
diagnose anything through a computer with out at least a modicum of
information.

...Ron
--
68' Camaro RS
88' Firebird Formula
00' Mustang GT Vert

07-29-2005, 18:01

I went to Autozone because my buddy is a manager there & he brought out
the battery tester... it's apparently in extremely good condition,
EXCEPT at idle with headlights on & A/C going full blast... it's
drawing about 4-5 amps (-4 to -5 displayed). I snipped the battery
cables & re-connected them to the terminals with new battery terminal
connectors... didn't help. I cleaned the battery terminals as well. I
also tightened all connections w/ the alternator (which was just 1...
the power wire..).

Any thoughts? This stinkin' red battery light remains illuminated.

-Mike

07-29-2005, 20:01

On Fri, 29 Jul 2005 17:24:35 -0700, memset@cellulean.com rearranged some
electrons to form:

> I went to Autozone because my buddy is a manager there & he brought out
> the battery tester... it's apparently in extremely good condition,
> EXCEPT at idle with headlights on & A/C going full blast... it's
> drawing about 4-5 amps (-4 to -5 displayed). I snipped the battery
> cables & re-connected them to the terminals with new battery terminal
> connectors... didn't help. I cleaned the battery terminals as well. I
> also tightened all connections w/ the alternator (which was just 1...
> the power wire..).
>
> Any thoughts? This stinkin' red battery light remains illuminated.
>
> -Mike

Apparently, your alternator is not supplying enough current to charge the
battery and run the electrical accessories.You really need to measure the output
voltage... why didn't your Autozone buddy measure it?

--
David M (dmacchiarolo)
http://home.triad.rr.com/redsled
T/S 53
sled351 Linux 2.4.18-14 has been up 23:31 1 user

07-29-2005, 21:01

memset@cellulean.com wrote:
> I went to Autozone because my buddy is a manager there & he brought out
> the battery tester... it's apparently in extremely good condition,
> EXCEPT at idle with headlights on & A/C going full blast...

There you go, life with a Fox Mustang. I have the new alternator
(3G) and at idle with the lights and Max AC it does the same thing.

--
"Network management is like trying to herd cats."
-- Unknown

"I wonder how much deeper the ocean would be without sponges?"
-- TazAmd - Humor Section Gettingtogather.com

07-30-2005, 04:01

So you're thinking the alternator could be at fault? I'll go to Hammons
Auto Parts first thing Monday (where I bought it) and let them test it.
Grrr.. what a pain in the ass =(.

-Mike

07-30-2005, 06:01

On Sat, 30 Jul 2005 03:43:17 -0700, memset@cellulean.com rearranged some
electrons to form:

> So you're thinking the alternator could be at fault? I'll go to Hammons
> Auto Parts first thing Monday (where I bought it) and let them test it.
> Grrr.. what a pain in the ass =(.
>
> -Mike

An alternator works by creating a rotating magnetic
field which cuts across a set of wire windings.
As Mr. Faraday and Mr. Maxwell told us, a changing magnetic
field intersecting ith a wire creates a current in the wire.
Since the field is rotating, the current alternates between
positive and negative and thus creats alternating current (AC).
Strategically placed diodes forces the current to go in the same
direction, thus creating direct current (DC).

The rotating field is created as DC current from the battery flows
through slip rings to a field winding on a rotor
that is spun by the belt pulley.

Some time ago I disassembled the alt. on my
Torino and installed a "hi-output" kit.. new brushes, different
stator winding, and some bigger diodes. If I am at a slow idle (stopped
at a stop light whilst still in drive), the alternator output will drop
enough that the voltmeter drops below 13 volts. The regulator leaks
enough current through the ALT light to turn it on just barely in that
case. Goosing the throttle makes it go back to normal.

The regulator is trying to put enough field current through the
rotor to keep the voltage up at low RPM. When it hits the maximum
current, the output voltage drops and the light comes on. The
OEM style regulator was only able to vary the field current
discretely, it had a relay inside that basically turn the field
on and off to maintain the output voltage. An electronic regulator
(which I have now) can vary it across the range of adjustment.

Guess what, 35 years later, alternators still work the same way,
except now the regulator is built into the unit.

I would take the unit back and have it tested. I haven't ever
had too much luck with generic auto parts stores alternators,
they don't really last very long. I would try NAPA.

Also, it's possible that they didn't hook it up right....

--
David M (dmacchiarolo)
http://home.triad.rr.com/redsled
T/S 53
sled351 Linux 2.4.18-14 has been up 1 day 9:01

07-30-2005, 20:01

I'll go ahead & pull the alternator out of the car & have it tested.
Thanks!!

-Mike