Battery light flashing

[Jingoist]

My battery light has been flashing when I cold start my truck.

It flashed erratically and then after 30 seconds to 2 minutes it turns off completely. It won't do it after the truck has been warmed up and driven or while driving.

At idle the voltage reads 13.83 and with the A/C and Radio blasting it went down to 13.55.

I'm thinking it may just be a fuse or a lose ground cable. I just can't seem to find where the grounds are or what fuse it could be. Batteries are two weeks old as well.

[AlaskanEngineer]

Saw something similar, but not exactly like this once due to bumping the exciter wire connector on the top of the alternator -(I had laid across the engine on a blanket to work on a turbo) anyhow it was making intermittent contact and caused some funny stuff with battery light. Worth checking quickly, thats the only idea that comes to mind outside of what you already mentioned.

[smokersteve]

I have the same issues. it is the alternator.

[WarChild]

Its ether your batteries going bad or an issue with your alternator. Get your batteries checked and then you will know.

[dfuzz78]

Originally Posted by WarChild

Its ether your batteries going bad or an issue with your alternator. Get your batteries checked and then you will know.

+1

I had the same thing happen; Alternator.

[Jingoist]

Originally Posted by WarChild

Its ether your batteries going bad or an issue with your alternator. Get your batteries checked and then you will know.

Well the batteries are brand new. I'm just stumped as to why the voltages are still acceptable, and it only happens when on a cold start.

[dfuzz78]

Originally Posted by Jingoist

Well the batteries are brand new. I'm just stumped as to why the voltages are still acceptable, and it only happens when on a cold start.

Your voltage regulator is starting to crap out. Unfortunately, it is part of the alternator, so the alternator needs to be replaced or rebuilt.

[Jingoist]

Originally Posted by dfuzz78

Your voltage regulator is starting to crap out. Unfortunately, it is part of the alternator, so the alternator needs to be replaced or rebuilt.

I just did a cold start right now, voltage was 12.58 cold, batteries went down to 10.60 while cranking, hit 12.2 until the alternator kicked in and then went up to 14. There was no battery light this time.

These voltages were all taken on the battery terminals. And like I said before, once I start driving the light never comes back on.

Is there a way to test the voltage regulator?

[dfuzz78]

Originally Posted by Jingoist

I just did a cold start right now, voltage was 12.58 cold, batteries went down to 10.60 while cranking, hit 12.2 until the alternator kicked in and then went up to 14. There was no battery light this time.

These voltages were all taken on the battery terminals. And like I said before, once I start driving the light never comes back on.

Is there a way to test the voltage regulator?

Yes, pull the alternator out and have it tested by a reputable alternator repair shop. Don't go to those autopart stores, their tests only last 5-10 seconds and our regulators show problems after that time, so their tests never show it.

I know it's not what you want to hear right now, especially after dropping a few hundred on new batteries. But we have been through this before and it ends up being the alternator. I chased and tightened grounds, replaced batteries, and had to go through 3 different alternators (autozone duralast crap) before the problem was solved. Save yourself time, effort, and headache and go get your alternator repaired or replaced. Try and stay with a Motorcraft alternator...
Good Luck

[Jingoist]

Originally Posted by dfuzz78

Yes, pull the alternator out and have it tested by a reputable alternator repair shop. Don't go to those autopart stores, their tests only last 5-10 seconds and our regulators show problems after that time, so their tests never show it.

I know it's not what you want to hear right now, especially after dropping a few hundred on new batteries. But we have been through this before and it ends up being the alternator. I chased and tightened grounds, replaced batteries, and had to go through 3 different alternators before the problem was solved. Save yourself time, effort, and headache and go get your alternator repaired or replaced. Try and stay with a Motorcraft alternator...
Good Luck

I had the batteries replaced for free under warranty, so that isn't a big deal, neither is taking out the alternator. Thanks for the info.