My 2004 f350 diesel is not charging the battery Alt. test good Bat. test good

The generator bat terminal should be hot all the time, is it? Use a test light to check. Did you check trouble codes for your charging system, there are codes listed for charging system, in database. Is this a rebuilt generator or brand new? It seems some rebuilders have trouble getting ford generator rebuilds, correct, according to my info.

If you are sure the batteries are charged up fully but you keep having issues with having to jump start I would double check the batteries after sitting for a while. Could be a problem that there is a short that is running the battery down enough not to work. Could also be your starter is pulling too much juice as if you put a boost with your battery hooked up you are using a lot more power than just your operating battery. Just a couple of ideas.

First make sure both battery cables are free of corrosion and ground is secured to chassis and engine then check to see if theres an alt. fuse or bat. fuse blown. Another way to test charging sys w\out an meter is to remove the ground terminal from the bat. with the car running, if the alt. is good car stays running, if all else fails take the alt and bat to a parts store that will test them for free

You need to fully charge the battery and load test it, then check the charging system and alternator drive belt for tightness. do not remove cable when running or it can harm the charging system...ok on older cars, no longer good practice. Quick check of charge system can be done with volt meter across the battery. Volts should read between 13 and 14volts and not drop over time. With all lights, heater etc on volts should be better than 12.5 (usually above 13 and again, not drop with time.

you dont slice any wire to the battery. the alt is turned on by grounding the green field wire on the back of the alt.THIS IS FOR TEST ONLY if you leave it grouned and drive it you will blow up the battery from all the hydrogen gas created by the massive overcharge. you also will damage every computer in the car from the overvoltage they will recieve.
the engine computer is the regulator for the alt.

If the light is on and the alternator is good then you either have a short to ground in the wire that runs the charge light or there is a diode in the alternator that is bad.The alternator will test good with a bad diode if it is only tested for the voltage it reaches but if you were to check the amperage output it would be down from it's output rating.

Thats a guessing game, but first, if the battery light was on, that means no alternator output. So recharge the batteries and be sure they are good, Then replace the alternator. If the batteries and the alt are good, and the battery light is off, then all should be OK.

How old are your batteries ? Diesels take a lot of juice to turn them over, I had a similar problem once, turned out to be the positive cable leading between the batteries.I would get a diagnostic on it to confirm your problem, could just be something simple.

Check brushes in alternator.

the ALT should charge from 13 v to 15.75 v less than that u need to replace the alt and u can check by ur self by use any voltmeter