supermario

Hello Guys, I know this is my first post and probably a dumb question to ask first time posting but here goes.
I have a 03 GT 4.6. the battery light went on and minutes later it died. I replaced the alternator with a new Ford oem one. It started up and ran fine for a day. Now the battery light is blinking once in a while at random times. I did search and my alternator shows its charging, I charged the battery with a battery charger and it shows its holding a charge, I made sure the plugs are plugged in all the way, the battery terminals are clean and secure. The belt is in good shape and doesnt appear to be slipping or damaged. So what next? I read to check out some fuses but I didnt know which fuses to check?
Any help would be greatly appreciated. And I cant wait to learn and be able to help someone myself one day. Thankyou

cliffyk

Have you done a high-current load test on the battery? A lot of FLAPS will do this for free, but make sure it's a 200A or better load test.

If you are a "tooloholic" like me HF has a great 500A tester for $80, often on sale for $50 to $60. This sucka' can really wring out a battery...

supermario

My brother has one of those testers and we tested it today. The alternator is charinging fine, even under load. The battery showed 12volts but when put under a load, it read "weak". We tested it at 3k rpm and with all accesories on. When Im driving and the light blinks off and on, the volt gauge shows normal. The last time when my stang died, the gauge showed low but now its not. Im under the impression i have a bad battery but I dont have any $ right now. I read there are some fuses to check but I dont know which ones?

WhiteFoxGT

Could be a cam sensor issue. I've heard of alts causing cam sensor codes, could be the other way around in your case. Im not saying toss sensors in, just putting the idea out there. Could be a faulty sensor wire, cluster...etc...

supermario

Since the alternator is charging and the battery shows its weak under load, wouldnt it just be as simple as a battery? Ive read that a bad alternator can ruin a battery and vice versa? I did just replace the alternator with a brand new OEM one from the dealer? Thanks for the help. Im gonna get a battery I guess and see what happens. The process of elimination is expensive

WhiteFoxGT

i musta thought you checked the battery... sorry about that last post of mine it was late and I was drunk

supermario

Well I replaced the battery with a new one. So Im gonna wait and see what happens now. I really hope its fixed. I checked it again today and shows its charing at 14V.

cliffyk

Here is the complete charging system diagnosis and testing section from the '03 shop manual.

supermario

Thanks for this info. Very helpful. I already replaced the battery and the light hasnt come on yet. Its only been one day though. Im gonna check fuse box too.

supermario

Ok guys, please help me out. I replaced the alternator, battery, fuses, checked belt, battery terminals, all connections to the alternator and battery, belt looks good, alternator is charging at 14v. What else, Ive pretty much gone through everythign but the battery light still blinks or comes on intermittantly. I give up, should I just take it someplace? I hate to pay $$. What do you think the chances of the new alternator not being 100%, perhaps I should return it to dealer and try another new one?

By the way, the gauge shows its charging, and there are no issues with power to the vehicle. When the car first died out, the charging gauge showed low when it died but it looks to be fine right now, even when the light is on.. Also I did check the charging system under a load. What else?