I have a 93 d350 that a couple of weeks ago "stopped charging" the gauge no longer showed that it had voltage and all the electronics in the cab quit working. I replaced the alternator and still nothing so I had it tested and they said it was good. I checked the battery to block ground and the alternator to block ground and they were both tight. I did the test where you remove the field coil circuit and run jumper wires to the battery and that did make it start charging it jumped to 17v almost instantly. I then did the test where you probe the field coil wires with a test light, test light to dark blue wire "positive" clamp to ground then test light to dark green wire "ground" and clamp to positive, both wires would light up the test light. Correct me if I'm wrong but this should mean everything in the alternator circuit is functioning properly. If the crank positioning sensor was not working it would not tell the pcm to send the ground signal and if the asd relay was not working I would not have power at the positive wire of the field coil. Also being that I had a ground signal this should mean that the regulator in the pcm is functioning properly. Is there something that I am missing? or is my problem something other than the charging system.
P.S. The battery was staying at a pretty constant 11.89v for about 3-5 minutes while the truck was running. Also my fass lift pump is working just fine, only the components in the cab of the truck stopped working. The wait to start light also stays on while the truck is running and the truck has no issues cranking over.