Alternator issue?

Tiny
CHRIS001
  • MEMBER
  • 2003 FORD CROWN VICTORIA
  • 4.2L
  • V8
  • 2WD
  • AUTOMATIC
  • 23,800 MILES
I have a 2003 Grand Marquis, I just put an alternator on its brand new. When I'm sitting still it charges fine.I push the brake and it goes down and doesn't charge fully. I let up its fine I put it in park charging fine. I push the brake and it went down again. I turned on the lights to see what it was doing that way I can see the headlights get a little dimmer and the alternator is pulling, and the alternator gauge is low. I let off the brake and everything is fine. Does that sound like a relay? Or electrical or something else maybe? The reason I was asking if it could be a relay stuck is also when I cut the car off the wipers will come on and take one swipe.
Tuesday, March 21st, 2023 AT 5:36 PM

10 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
Hi Chris,

when you press the brakes or use the headlamps, the voltage will drop. I need to know how low it drops, so I need you to perform a test.

I want you to test the alternator's output to make sure we have a good one. New or not, it can be faulty.

Here is a link that explains how to test one. All you will need is a voltmeter or multimeter. Follow the directions in the link and let me know the results.

https://www.2carpros.com/articles/how-to-check-a-car-alternator

Also, make sure the battery terminals are both clean and tight, the battery cables are in good condition, and a quick inspection of grounds.

Let me know what you find.

Take care,

Joe
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Tuesday, March 21st, 2023 AT 7:58 PM
Tiny
CHRIS001
  • MEMBER
  • 44 POSTS
Well, what I have noticed is an example if the headlights are on and it is started or if the headlights are off and it's started in park sitting the voltage is right in the middle where it should be. If I back up and stop or push on the brake the voltage meter will go way low. If my foot is on the brake I mean drop from the middle to the bottom. Only if I push the brake, if I never use the brake or apply a load or pressure, it's fine. I will check those battery cables in the morning because they may not be on tight. Also, I noticed I got a turn signal that will work regular for a long period of time then it will go out but it's not a bulb that may be something different.
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Tuesday, March 21st, 2023 AT 8:07 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
Hi,

Let me know what you find. Also, I'm concerned if the gauge drops off completely. To me, that sounds like a connection issue failing rather than a faulty alternator.

Check the connectors at the alternator as well.

Let me know.

Joe
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Tuesday, March 21st, 2023 AT 8:21 PM
Tiny
CHRIS001
  • MEMBER
  • 44 POSTS
It gets very low even if I stop at a stop sign and take off it will drop pretty low for that time. So, it's like if I hold my foot on the brake it overloads the alternator. It's like push it down it overloads it let off of it its fine. I can pump the brakes in park, it will be in the middle when I let off the brake and extremely low when I push on the brake.
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Tuesday, March 21st, 2023 AT 8:36 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
Hi,

Chris, I need you to check the output. The brake lamps don't draw that much voltage. At this point, I have a theory that we have a weak connection that causes this to happen. On the other hand, if you load the alternator with the brake light and the voltage at the battery doesn't drop, that is the likely cause.

If the alternator does drop, then I suspect it is a faulty alternator.

Just for a test, turn the wipers on and see if the same thing happens.

Let me know.

Joe
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Wednesday, March 22nd, 2023 AT 5:45 PM
Tiny
CHRIS001
  • MEMBER
  • 44 POSTS
It does the same with the wipers on. I'm thinking it could be a connection or since it's when I push the brakes, maybe a wire in brake lights.
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Thursday, March 23rd, 2023 AT 5:41 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
Chris,

It could be a general grounding issue, but it wouldn't be a power supply. If it was, it wouldn't affect all electrical components simply because they receive power from different fuses. For example, the brake lights and the wiper motor gets power from different places.

By chance, do you feel comfortable performing the alternator test I attached above? Also, with the engine running and the lights on, see if they dim if you move the negative battery terminal around.

Let me know.

Joe
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Thursday, March 23rd, 2023 AT 4:36 PM
Tiny
CHRIS001
  • MEMBER
  • 44 POSTS
Right now we are getting some bad weather but when it clears in a few days I will test it just to make sure.
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Thursday, March 23rd, 2023 AT 6:58 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
No problem, Chris. Let me know how things turn out. As far as the weather is concerned, we are getting storms at this time as well. Ugh! I want some warm summer days. LOL

Take care,

Joe
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Thursday, March 23rd, 2023 AT 7:37 PM
Tiny
CHRIS001
  • MEMBER
  • 44 POSTS
Me and you both, it's supposed to be really bad here tonight. I'm ready for some fishing and summertime activity. Right now, it's like mother nature is having a custody battle with winter, lol, but good days are coming!
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Friday, March 24th, 2023 AT 7:43 AM

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