alternator has me stumped
Thread Starter
Abby Normal
Joined: Dec 2001
Posts: 53,462
Likes: 92
From: Press "2" for English
alternator has me stumped
i can't seem to get the alt to charge. i took it off recently and tore it down and checked everything (except the reg). the bridge rectifier was suspicious as one diode gave a fluxuating reading. everything else checked o.k. i reassembled and took it to autozone and they spin tested the alt and it checked o.k. there as well. their machine apparently can even check the rectifier and VR individually.
so they say it's o.k. and i put it back on the car. just to make sure it's not a power issue, i take a known good 12v source and tap into the #1 wire on the side plug. still no charge.
at this point, i'm back to suspecting the alternator again. anyone else have any other ideas?
so they say it's o.k. and i put it back on the car. just to make sure it's not a power issue, i take a known good 12v source and tap into the #1 wire on the side plug. still no charge.
at this point, i'm back to suspecting the alternator again. anyone else have any other ideas?
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
Well, there are two wires going to that alternator from your harness. One is a red one that's 12V constant, and the other is a switched 12V. That one is the sense wire, leading in from the dash.
Do you have a GEN light on the right side of your center gauge cluster?
Do you have a GEN light on the right side of your center gauge cluster?
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
Just a month ago ... lincoln town car alternator.
The lights on dash & headlamps would routinely dim for a second or two ... but apparently it always kept the battery charged well enough. But it worried me.
I had to change out the infamous leaking 4.6 plastic intake ... with alternator off, it was great time to have Alt checked.
Took Alt to autozone ... they spin tested & tested diodes etc ... it checked out AOK.
I went straight to a friend's alternator-starter-clutch rebuilding service.
Alternator had a bad diode.
Replaced entire internal regulator.
Works perfectly now.
I know I got the friend price ... $48 ... cheap insurance at double that.
Autozone spin test ain't absolute ... a pro is.
The lights on dash & headlamps would routinely dim for a second or two ... but apparently it always kept the battery charged well enough. But it worried me.
I had to change out the infamous leaking 4.6 plastic intake ... with alternator off, it was great time to have Alt checked.
Took Alt to autozone ... they spin tested & tested diodes etc ... it checked out AOK.
I went straight to a friend's alternator-starter-clutch rebuilding service.
Alternator had a bad diode.
Replaced entire internal regulator.
Works perfectly now.
I know I got the friend price ... $48 ... cheap insurance at double that.
Autozone spin test ain't absolute ... a pro is.
Last edited by jackson; Apr 17, 2007 at 09:49 AM.
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
The spin test is the more often than not incorrect. They will get a much better result if the alt is in the car and they can test it while it's running.Even better is a shop that specializes in stuff like that. Problem is, and I have this problem...not everyone has a local specialty shop.
Thread Starter
Abby Normal
Joined: Dec 2001
Posts: 53,462
Likes: 92
From: Press "2" for English
Thread Starter
Abby Normal
Joined: Dec 2001
Posts: 53,462
Likes: 92
From: Press "2" for English
the question i have for you though is are you telling me the two pin connector has #2 constant 12v while #1 is switched?
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Drifting
Joined: May 2005
Posts: 1,629
Likes: 4
From: Somers CT
I remember we used to have to "Flash" the Generators on a car after they were rebuilt to get them to charge, I've never had to do that with an alternator but I ran across this article that implies you need a little rpm to set the mag field after the've been sitting. Also need a good 12v source. Maybe the source line has a fault/open??
Since alternators don't have a large mass of magnetic
material in them like a generator, they need an
external source of power for the "field flash" that
gets them started charging. Without that (provided
from the ignition switch via the warning lamp
filament) and alternator that's been idle for even a
few days may not put out until the engine is buzzed to
a high RPM, if then (not attainable by bump-starting).
Generators can sit idle for many months before they
lose all of their residual magnetism - at which point
they require polarization - so even with NO battery in
the car it's possible to bump-start a
generator-equipped car, but you still have to get the
thing above the "cut-out" speed of the regulator
(approximately 760 engine RPM)
Since alternators don't have a large mass of magnetic
material in them like a generator, they need an
external source of power for the "field flash" that
gets them started charging. Without that (provided
from the ignition switch via the warning lamp
filament) and alternator that's been idle for even a
few days may not put out until the engine is buzzed to
a high RPM, if then (not attainable by bump-starting).
Generators can sit idle for many months before they
lose all of their residual magnetism - at which point
they require polarization - so even with NO battery in
the car it's possible to bump-start a
generator-equipped car, but you still have to get the
thing above the "cut-out" speed of the regulator
(approximately 760 engine RPM)
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
Former Vendor
Joined: Nov 2005
Posts: 683
Likes: 1
From: Mounds View Minnesota
There needs to be 12v on the brown wire and the small red wire.
The brown wire needs to have resistance, either a gen lamp or a resistor wire.
The small red wire is the sense wire. It connects to the junction, splice or horn relay depending upon the year of your car. The place this wire is connected it the place that will have the proper regulated voltage and is where all power should be taken from
The brown wire needs to have resistance, either a gen lamp or a resistor wire.
The small red wire is the sense wire. It connects to the junction, splice or horn relay depending upon the year of your car. The place this wire is connected it the place that will have the proper regulated voltage and is where all power should be taken from