Hi, I decided to give my car a tune-up and removed the positive battery cable instead of the negative by accident and now the charging system isn't working. I replaced the ECU, alternator from Autozone and it still isn't charging. I hooked up a meter and it charges on and off like it wants to charge, but detects something isn't right so it disengages and does this over and over. I checked and cleaned all the grounds that I could see. What else could it be? Thanks.

 

How are you determining it is not charging?
If the battery state of charge is around 80% it , the system, may not feel it needs to be constantly charging.
Are you putting on some type of load, A/C , hi beam etc., to create a load? What does it do then?
Anytime someone changes an ECM without programming the replacement scares me and also opens the gate for a multitude of problems.
Some alternators,,,,,,,,,,,,,,,,,never work right out of the box.
The more things you touch the more things that can go wrong.. This is where guessing gets expensive and sometimes disappointing..

 

I'm diagnosing this car for my brothers friend. It isnt my car. Not exactly sure how the system functions on these models. I assume it should just keep the battery at 14v at all times. I didn't not turn any loads on and it seems to be dying as it goes below 12v after a few mins of idling. You can hear the alternator excite in and out during idle. Is this normal because the battery is still dying and it is new too.

 

Need to know where you are taking your voltage readings.
At alt output terminal, the battery, or somewhere else.
You can get different readings at those places even with a proper functioning system.

 

I'm getting them directly from the battery. Also were you saying this system only engages charge under a load and not all the time? Never seen that before. I'll check readings again and post more precise voltages at the terminals mentioned when I go back to my bro house. Thanks again.

 

Hello,
Did you figure this out? My Ford Five Hundreds charging system light came on and turned off as it malfunctioned and then would work and stop again. It's in the Dealership and has been elevated to level two engineers. So far they have not been able to figure it out. So far they have installed two alternators.