Battery light flickering

TropicMustang · Nov 30, 2009

My battery light tends to flicker when it is really cold outside and when I am at wot the light flickers even more. During normal driving it dosent flicker though. What is the problem?

wmburns · Nov 30, 2009

belp slip

Nice sig. What year?

Assuming that the alternator has been tested and is good, look for evidence of belt slip (black power around the pulley). Are all of the idler pulleys in place?

Also, check fuse F1.5 (15a) in the Central junction box (CJB).

Check the small wiring connector to the alternator. Plugged in good? Clean?

ChillPhatCat · Nov 30, 2009

I'd say alternator is just starting to wear out... when it's really cold out, your battery tends to drain faster and probably puts a little more strain on the alternator right after you first start it up. I'd say it's unlikely to be belt slip because cold causes things to contract, not expand... so it should be tighter and be less likely to slip when you first start the car on a cold day.

TropicMustang · Nov 30, 2009

thanks It's a 2000. Im going to replace the alternator tomorrow and hopefully that fixes the problem. Im trying to get this situated because im heading out to AED out here in sacramento on s:aturday for a tune so i can get some numbers.

Kilgore Trout · Dec 1, 2009

I agree its belt slip. Does not make sense to replace the alt first, replace the belt!

wmburns · Dec 1, 2009

The truth of the matter is that it could be a weak alternator, weak battery, or belt slip. IMO it is more likely to be a bad alternator. Which is why the 1st suggestion was to test the alternator.

As RPM's increase, more power is needed to run the engine's electronics. If the alternator is boarder line, the extra power requirements could push it over the edge.

Reminder, the battery light is driven off of battery voltage only. Further, the PCM reduces charging current at WOT (to save load on the motor). Consider if the battery is weak or the terminals are dirty, when the alternator output is decreased by design, the extra power has to be made up by the battery. This could overwhelm the battery's ability to keep up.

That is why it is also good idea to check/clean the battery terminals at the same time. Ensure that the top of the battery is clean as well. Todays car will not run without a solid battery.

Belt slip should be evident on the belt and around the pulleys. But, IMO, what makes the most sense is to TEST the alternator first. Almost any auto parts store will test your alternator for free. Many will do a basic function test with the alternator still on the car.

While the alternator is off, INSPECT the belt looking for evidence of slipping/cracking/wear. If found, replace it. Also, inspect the tensioner. Replace it if it is weak.

To recap, the absolute 1st thing to do should be to clean the battery terminals. Clean the top of the battery. Next, take your car to the auto parts store. Ask them to test your battery and the alternator. Go from there.

twogts4us · Dec 1, 2009

Alternator - have tested and replace if needed. The Sn-95s are known to eat alternators. (or Ford just installed crappy ones)

GDawg · Dec 1, 2009

twogts4us said:
Alternator - have tested and replace if needed. The Sn-95s are known to eat alternators. (or Ford just installed crappy ones)

I'm into my second one after 75k miles (and eleven years) but they ARE expensive if you stick with Motorcraft. I was lucky to find a good one at the junk yard.

TropicMustang · Dec 2, 2009

swapped the alternator today and it fixed the problem.

Ateup · Dec 2, 2009

TropicMustang said:
swapped the alternator today and it fixed the problem.

I bet he meant to thank all you guys for your help but forgot.

TropicMustang · Dec 2, 2009

Yes, im sorry. Thank you everyone for the help. I also got a fresh battery in today, to replace my crappy autolite.

Kilgore Trout · Dec 3, 2009

What kind of battery did you get?

Mike97gt · Dec 3, 2009

TropicMustang said:
swapped the alternator today and it fixed the problem.

thanks for reporting back on what fixed it.

TropicMustang · Dec 4, 2009

I work at Les Schwab so i got a Les sSchwab battery made by JC whittney. Its the top of the line version the XT. 84 month Waranty and i get a screaming deal on it so its a good deal.

soupnutz · Dec 5, 2009

wmburns said:
That is why it is also good idea to check/clean the battery terminals at the same time. Ensure that the top of the battery is clean as well. Todays car will not run without a solid battery.

A few years ago I started putting a thin layer of vaseline on the battery posts then after hooking up wires put another thin coat on the terminals.

After a week or two I would start to get corrosion build up. Since using the vaseline, never any corrosion whatsoever, looks brand new.

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