Hey all, howdy. The battery warning light on the dash is staying on. The battery tests good; has 12.5 volts with the engine off. I think the alternator is okay, reads 14 volts with the engine running. My scanner tests indicate battery and alternator are both good.

It's a 2001 F150, 4.2 V6. This happened immediately after I replaced plugs and plug wires.

Has anyone experienced this problem? Any advice, or where to look or what to do?

Thanks in advance

 

many threads on this issue (vehicles in general, not specifically the f150), with the common suggestion being to get the alternator tested, as the diodes may be bad.

 

Check the wires around the alternator, something may have been knocked loose or there may be a bare wire touching ground around the alternator. If that is ok, I would have the alternator checked, since your regulator s built onto the alternator. Sounds like something is wrong with the regulator.

P.S. Some of the newer vehicles have a small fuse that feeds the regulator circuit in the underhood fuse box. If you have one, make sure it's ok.

 

Make this simple:

Ignition OFF.
Disconnect 3-wire plug from alternator.
Turn ignition to RUN (not START).
If the light is still on, you have a shorted wire to ground.
If it's off, the regulator in the alternator has failed.

 

Thanks very much for the replies. In the morning I'm going to try these suggestions, and I very much appreciate your help.

 

I want to be very clear about my diagnostic responses to your issue.
1.You saw no Codes I knew had to be present at some time and specified them. I was correct!
2. Based on your measurements, I described the system actions. I was correct again.
3. They pointed to the Alternator. >This is correct under the final codes listed< even if the Alternator is not faulty, it cannot function under the listed codes conditions described.
4. Code 625 is Field Control Circuit open The Alternator cannot function without the Field Winding Control Power to (vary) its output. power
5. Code 65B is Alternator performance >range. That is exactly what you have. causing poor performance of the system.
Sorry you changed the Alternator, but I did say >pointed to the Alternator. It cannot function without the Field power control no matter why!
Bottom line is the code must be seen, description read and understood, and circuit function known.
This why I was pushing earlier in the thread.
What you do get from this is the system has a fall back feature that allows the Alternator to function at a minimum level to prevent total failure, noticed by message, until its repaired. This is the code 65B.
.
Too many just jump on a faulty Battery before they even do any diagnostics to find out.
Imagine if your Doctor did things without diagnostic based actions.
Good luck.