Ok, first I've read every thread here on this. I charged the batteries fully, new alternator put in and checked grounds. Light was off,mbut while driving to work it came back on again and stays on. Battery voltage is 14.2 on each at idle and 13.4 while engine and key off. I'm stumped here. Maybe the two prong connector needs to be replaced? Any ideas?

 

What is the voltage at the batteries @ 2000 rpm with the light on? Also are you sure the Batts voltage is that high not running? It should be around 12.6v. Make sure the connections of the smaller red wires at the terminals are clean.

 

I'll double check the terminals. So here is an update. Now the bat light comes on and off for various time periods. Just checked bat voltage at idle and it was 13.94 on each. I had no acc running. Didn't have this problem at all until the alt went out. Replaced it with a new ultima 110 amp alt (I know need more amps) and now have the bat light on intermittently. Both bats load tested fine. New alt I had tested before installing and it was ok. I'm dumbfounded. I'll check all terminal connections and ground straps when I get a chance, but this wasn't an issue until the alt change. Thanks for any input.

 

You need something to monitor the voltage when the battery light is on. It can be with a power port voltage meter, using an adapter like this to attach a voltmeter



Or run leads to the alternator or batteries to have the voltmeter in the cab.

Your batteries may be up ar 13+ right after shutdown, but they quickly will drop into the 12v range.

You also need to post info on your truck so we know if the gauge cluster is involved in controlling the alternator.

 

Update. 2005 F350 DRW FX4 6.0 diesel. Battery light on intermittently. Changed alternator, load test on bats fine. Bat voltage key off 12.6, Bat voltage at startup 11.6 each, after glow plug off 13.9. Noted no voltage change when bat light on at the bats. Still waiting for a ordered voltmeter for in cab, but the light comes on and off. Any ideas as to why this keeps happening. All terminals cleaned, grounds look good and clean. gauges all working even when bat light on as well as other acc. I'm totally at a loss as to the cause. And is it still safe for the Ficm to drive like this? Any suggestions. Thanks

 

Hi Doc -

You've gotten some good advice here already. Your issue could be as simple as the connector on the alternator that taps into the factory harness. Have you inspected that plug for pin issues?

FICM's are incredibly sensitive to supply side voltage inadequacies and fluctuations. I'd try to get the issue resolved as soon as you can to avoid the FICM issue you are concerned about.

Hope this helps!

 

Update for those interested. Went back and rechecked every connection, even redid the connector on the back of the alternator. All connections cleaned and redone. All grounds cleaned and redone. Even checked the OD wire to ensure it wasn't grounding. Checked absolutely every connection and all good. Did a ripple test on the Alternator and it was fine at .0086. But still had a bat light on. Checked bats again and noted that with acc on bat voltage would drop to 12.5, was looking around on the net and found another type of test for the alternator. It's called a resistance test. Disconnect the alternator to battery cable and use multimeter to check resistance between alt post and the wire. Should be less than .05 milliamperes. If it is higher, the. You have a bad diode that none of the other tests would show. Mine was greater, so got a third alternator. Tested it before install and all good and retested after install and all good. Turned truck over and bingo, bat light went out. Now getting 14.5 at the bat even with all acc on. Thanks to everyone that helped and hope this info helps someone else.

 

Thanks for the update, so many do not.

So another situation, I'm going to assume, of a new rebuilt alternator being a problem out of the box. You would mind updating of the alternators source?

 

There are just SO many situations like this. The hassle factor alone is HUGE. Stop buying reman alternators, people. It's just not worth it.

Very glad that you're up and running again! I'd suggest keeping a close eye on the FICM at this point for the next several months.

 

As requested. The alternators used were Altima. The last one was a motorcraft that was rebuilt by Altima. The new one I have right now is also and Altima. They are from Oreilly's and have a lifetime warranty. While I'd prefer a DC Power, it's not in the wifes budget right now.

 

Ruh Roh.... That's what I put in our Expedition, but it was a new one (they are actually called Ultima). We bought a New Autolite from Kragens before they were bought by O'Reilly, and it had a Lifetime warranty. It lasted maybe 24K and O'Reilly honored the Kragen warranty and gave us a New Ultima Select. I was thinking it was great because the factory original was like 110A and I think the Autolite was too, but the latest one is a 130A

We'll see, only have 6K on the Ultima but so far so good...