battery light blinking eratically

[ford diesel power]

I noticed my battery light blinking eratically the other day. it only blinks when the headlights are on but when i go up a hill or raise the RPM's it goes away. Then when i start coasting it starts again. The alt is a month old, one battery is 3 months and the other is 2 years old. Any help please???

[bigcountrysg]

Check the batteries, and cables. You should replace batteries in pairs. Because if you have a bad a battery most likely the other is bad too. If you replace just one battery. The older one will cause the new one to work harder and prematurely fail.

Have the batteries and alternator tested. Another thing to check is the belt if it is old it maybe slipping.

[ford diesel power]

am i the only one with this problem??? please help me. the battery light blinks eratically only after the headlights have been on for longer than 10 minutes.

[Bigdave196]

First off.... New or remanufactured alternator? Pep-boys/Autozone/Checker alternators all rebuild/reman the alternators, very rare to get a "Brand New" one from them. Just cant beat the warranty, but as all reman parts, they can fail. Dont get me started on how many starters I replaced in my 6.0's but lets say that I can do it in 15 min on my back in the middle of a parking lot with the 3 needed wrenches that always remain in the glovebox till I sold the trucks.

I concur with replacing batteries at the same time, but If I am not mistaken a flashing light for the battery is a sign that the charging system is failing and most likely your newly purchased alternator failed. I had to replace my alternator on my F-550's every 6 months on the average and batteries annualy. I did the AutoZone "Free Lifetime warranty" for the alternators and the Premium batteries with a 3 year free replacement warranty because it never hit my wallet again after that. Far better to cry once then several times to save a few $$$.

My reccomendation- clean all 4 terminals/posts very well, get the red/green anti corrosive doughnuts for the posts, get the red spray coating to protect the terminals from corrosion, Replace the other battery.. take the alternator back and exchange it and inspect the fan belt for all the little cracks that show its age...If needed replace as well.

Far better to cry once then several times because you wanted to save a buck.

[ford diesel power]

thanks or the info but my battery light never blinks when my headlights are not turned on. I drove 5 hours the other day non stop trip and it never blinked once. if i turn my headlighs on for 10 minutes that's when it starts blinking.

[Bigdave196]

Your Alternator is failing and your battery (the older one) is most likely trashed. Have both batteries checked to make sure that the new one isnt already damaged.

You drove 5 hours with a less than average load on your electrical system (no headlights) and it never blinked. 10 min after you put a demanding load (headlights) on your charging system the light started to flash because the alternator could not regulate and produce the required power to run all of your trucks electrical systems.

The following things will happen if you dont replace the alternator and other battery:

1. The weak battery WILL fail completely (I would bet that you have 1-2 bad cells already),and cause the good battery to try and make up for the loss of the demand for power by further stressing the good battery and causing premature failure. This will cause the cells in the good battery to rapidly go bad and not hold a charge. This will also cause your truck to start cranking slower than normal because there isnt enough power in the batteries to power the starting/glowplugs/fuel systems properly. Its a snowballing effect. Soon your truck will just barely start and the next time it wont.

2. Alternator will continue to fail and will further stress your electrical systems also causing stress to your systems because there is not enough power to support the whole system. Your alternator takes roughly 15 min to fully recharge your batteries back to optimum levels after a cold start. If your alternator cant properly recharge your batteries and also provide replacement power for the systems drawing power to run your Truck/AC/Radio/Lights/ ect...ect you will not only kill your batteries (doesnt matter if they are new or not) but you will also be left stranded somewhere.

Replace the battery and the alternator immediatly.....why are you still reading this, go get this done. Take the tools with you to AutoZone and do it in the P-lot if you need to.

[ford diesel power]

The problem was not the alternator. It was the terminal on the passenger side battery. Thanks for the help though.