KW T2000 Electrical Gremlins

Yeah, I'm used to automotive ECU's which only supply milliamps through a circuit for open circuit diagnostics. I was initially using a non-LED test light because those typically require enough current that they'll pull a diagnostic signal down and not turn on but the test light came on as if it was connected to the batteries.I was measuring the voltage on the board, they've got these huge solder balls, my guess is old school through board vias, but the ground still supplies 12V. Other thing I found is the dash, gauge panel and A/D converter all share a 20 amp fuse, I've got good power to the dash but not to the gauges, I'm wondering if they're stuck in a sweep mode because the A/D converter isn't getting power.

 

Thank you very much sir, I appreciate all the information you've given, I was about to give up and send it to the dealer, quite literally a lifesaver. The first few pages of the troubleshooting guide explain my exact problem, thank you so much. I did electronics manufacturing for a short while a couple years back. You pick a few things up as you go, never got past the hobbyist level though. I'll make sure to keep this thread updated as I figure things out, as I've learned with this truck, things are never what they seem.

 

I've been digging through the electrical for the last couple of days. I believe the A/D converter is dead, but I'm also wondering if that's a side effect of the short circuit. According to the diagnostic guide the signal wires should be no less than 2.5 VAC and I am only getting slightly over 1VAC. I've decided to put the gauge cluster issue to rest for now as it might not even be a problem.
For the short circuit I've resorted to pulling all fuses and checking for continuity to ground for each circuit, if I can find the shorted circuit then I can fix it or leave it unplugged. Its has gotten to the point where I drive with the alternator unhooked because it gets too hot and stops charging.

 

My long lost short has been found and fixed, the fuse panel continuity check helped narrow it down to daytime running lights, luckily truck only operates stateside so I believe they aren't required. Pulled the fuse and the short dissapeared and the battery will maintain a charge.

Now I cant get the alternator to charge the batteries, its bloody aggravating never seen an alternator fail like this. With the dmm directly on the Bat+ terminal, the voltage will hover around 11.8 then shoot up to 12.3 then down to 11.6. Not even over a duration, it happens in the refresh rate of the DMM, so each time the display updates I've got a different number that's completely different from the last. Raising RPM stabilizes it at some voltage, I was stable at 12.2 last I checked at 1500rpm. I'm pulling the alternator out tommorow and getting it tested at a rebuild place. I'm lost, I've never seen an alternator fail like that, they're either dead or weak and will only charge at high rpms, but this doesn't fall under either, its almost as if one if the windings is dead in the alternator. Any advice or suggestions on where to look or next steps?