Was your car having the same type of issue? I havent had the chance to take the alternator in for testing yet.

 

Whenever I read a thread like this, I always chip in and say to check your ground wires. The ones under the hood can be corroded and you won't see it unless you remove them and look underneath. A few minutes to run a little emery cloth over them to clean them up could be well worth it.

I've had a similar issue in the past but cleaned my ground connectors and replaced the Motorcraft battery with a Optima Red Top and haven't seen an issue in about 3 years.

I was doing some other work on the car this past summer and decided that since I would have the intake manifold off to replace the Charge Motion Control Plates - to replace the alternator with a PA Performance one from AM just to be sure I wouldn't have future problems.

Mine is pretty much a Garage Queen and doesn't get driven all that often so I keep a Battery tender hooked up most of the time, too.

 

Just to add, I had a Mazda 3 that had one of the wire work loose from the air intake sensor causing similar issues.

 

When they get weird all sorts of bizarre things happen and everyone's issues aren't all the same. The first one I replaced had issues that sounded much like yours. The second one I replaced tested fine under a load, but all the lights pulsed at idle. I am betting it was a bad voltage regulator.

You can try to figure out exactly what is actually wrong (I know electrics and wanted to know why too), but be prepared to invest some time -- or you can just replace the alternator in 20 minutes and cruise around with a smile on your face because it works now.

 

Don't know if I mentioned it in my original post, but the battery light in my dash will come on say, during startup or at an idle and will go away as I'm driving. I've already checked for loose grounds, everything seemed fine. I'll go ahead and double check and wipe down and ground contact surfaces and re-check the battery connections.

 

That sounds like an alternator issue. Low RPM = no charging....