I am having a huge issue with my truck not charging. There is only about 12 volts coming from the post on the alternator and the truck will run fine until the ignition system and other electronics run down the battery. It is a 1999 ford f250 super duty with the triton v10. I have already replaced the battery, battery terminals, alternator (had it bench tested twice), cleaned up all the grounds and connections, made sure there were 12 volts going to the two wires that go to the voltage regulator on the back of the alternator, checked the belt tension, and checked all the fuses. I am now leaning towards the ecm being shot but am not positive. Any insight would be greatly appreciated!

 

when running what kind of voltage are you getting accross the battery?

You said you tested the alternator...did you test it on the truck? Command max output? If so what did you get?

That is where I would start.

 

I had the same vehicle ('99 V10) with the same problem. The battery light came on very dim. I was not charging fully. Change the battery (1x)and altenator (4x). Then the light would get bright and then dim. Come to find out I had a break in the wire from the altenator back to the relay (starter relay, I think) that is located on the left fender well. I had a garage mechanic work on it since I was on the road and he could not find the break. Was able to charge the bat and drove home which was an hour away. Took it to the dealer and they found it within 45 min. Hope this helps.

 

Those alternators are famous for having bad plugs, so that would be first thing to check. Bench test is not full test. I had my rebuild alternator malfunctioning on rare occasions and it passed bench test, dying permanently month later.
If the post on the alternator shows 12V, than likely the issue is with alternator, but bad connections can be a nightmare to track.

 

Im getting a reading of 12.12 volts at the battery and 12.09 volts at the alternator. I'll have to check the wires to the starter relay. Thanks for the tip Coz77 that sounds like the extent symptoms of my truck to the tee. At the risk of sounding stupid is there a voltage regulator in the ecu? Thats what a guy at my shop is telling me and that I need a new ecu

 

voltage regulater should be internal to the alternator for that year.

Bad alternator.

 

its not the alternator. i bench tested it twice and swapped out another alternator from a service truck at work, that i know works, and it still didt charge. Im going to bring to to a repair shop tomorrow so anymore suggestions would be GREATLY appreciated!

 

The PCM (ecu) has nothing to do with the alternator (unless it's a dual alternator on a diesel).

There are 3 or 4 possibilities.

1) The alternator is bad
2) There is no power to the A wire.
3) There is no power to the I wire.
4) There is a problem with the stator wire.

The first diagram below tells you what you should see at the A, I and S wires (the 3 wires at the plug) as well as the B+ terminal under a number of different conditions. These are tested with alternator plugged in, by probing through the back of the connector.

The second diagram is the alternator wiring diagram for your truck.

 

Better check to see if the BATT light comes on when you first turn the ignition switch from OFF to RUN. You might have a blown fuse F29.

 

Question: I have a 2001 Ford F250 with 5.7L engine. The 3 wires in my connector are yellow, green, and orange. I don't have a white and black wire. Would you happen to know where I can find the drawing?

Thanks, Steve