I have a 1991 dodge ram b250 replaced battery alternator check fuses checked wires an still no juice from alt can my ecm be bad

USA car? 3.6 not 3.7:
so did you do all the tests, ??????
belt not lose,
13.3vdc to 15vdc and never less. running.
right, idle is 800RPM never ever less.
all fuses good for sure to PCM brain.
the PCm many be the ALT Regulator, you do know that fact too.
the alternator has a huge fuse off its huge wire stud cable. at ALT and must not blown out.
no scan tool fixing modern cars lacking scan tool is FAIL, hard
it will tell what is wrong if you'd just look.

P0622?? DTC errors means gen field dead.
the alt is for sure external controlled says BOSCH.
and the shop manual too , simple yeas, just 3 parts
no counting bad wire, top thing is fusable link.
see vast noob swap a gen, and not pull battery neg -lug first
and blow the fuse link to H3LL. or make it look burned and 1/2 dead.
bottom left is PCM , bad. both G grounds must not be rusty.
ok. count the 4 connections. and none bad.

depending on the code giving by the pcm is how you approach the diagnosis but in general the computer pulse width controls the field circuit in the alternator. #1 check for battery voltage at alt larger wire and then test for power at the two rear small wires remove control wire from back of alt then place jumper wire from alt terminal to ground monetarily is should charge if not alt is bad. if does you have a broken wire to pcm.

If the battery stays up and you have no other problems could just be a lose connection dont worry about it.

My 1992 Cummins W250 auto trans turned out to be the Computer/ECM mounted on front fender by battery tray. Mine only acted up in cold wheather. It started out with the ASD (auto shut down relay) clicking rapidly. In addition the water in fuel, wait to start and check engine light also blinked fast. In this state, the battery would not charge.

Check output from alternator with a voltmeter it should be between 13.8 to 14.7 if so then check at battery if it is not at least 13.8 minimum to be charging then the big wire on back of alternator is not getting back to the battery through ammeter gauge in dash.
I have hooked a wire from back of alternator straight to the plus[+] side of battery to fix that issue.
Sometimes ammeter gauge burns out breaking the circuit from the alternator back to the battery.

THERES A SIGNAL TO THAT OPERATED ON CURRENT FROM THE ALT OT THE ECM. CHECK IF ITS LOOSE OR MAYBE THE INTERNAL PART OF THE ALTERNATOR IS DEFECTIVE. THERES THE (RED) THICK WIRE TO CHARGE AND OTHER THINNER WIRES THAT SIGNAL'S THE ALTERNATOT OPERATION. DONT WORRY NOT BECAUSE THE ALT IS NEW OR REMANUFACTORED IT DOESNT MEAN ITS IN 100% WORKING CONDITION.... THEY FAIL ALSO WHAT EVER YOU DO REMOVE THE POSTIVE AND NEGATIVE WIRE BEFORE ETTEMPTING ANY WORK. ITS A BAD HABIT TO REPLACE A ALTERNATOR WITH CURRRENT ON.

check all the fusible link wires on battery(s) and leading to fuse panel!!

These trucks do have a regulator. But most importantly check all of your grounds. One bad ground can mess up an entire electrical system. Especially the charge.

It has got to be a bad short to ground some where from the regulator to the fuse box? Or the Alt. your useing is not the right one for the truck.

the numbers are 12, 41, 55
12- direct batttery inut to controller disconnected within last 50 ingnition key-on cycles
41- alternator field circuit- an open or shrted condition detected in the alternator control circuit.
55- final code - indicates the end of the scan codes

I've replaced the alternator and checked all the wiring still can't find the solution. I've posted to find out if the alternator control circuit can be repaired.