RVC (regulated voltage control) constantly charges the battery at 14.8-15.2 volts. It should cycle down to 12ish when the battery is charged. It was causing overcharging that made the AC work intermittently, the engine was overheating, and the positive battery connection was corroding.
I unplugged it and let the alternator self regulate which caused it to charge at 13.6-13.8 constantly, but gave a service charging system error most of the time. Corrosion, overheating and AC issues stopped.
Today the radio was in Demo mode when I went to the truck which is not normal, and since I had a minor slow start Saturday morning and evening, I assumed the battery was low. It took a few seconds longer than normal to start and I could hear it was turning slow, but when started it was running fine. Voltage meter on the dash was pegged out on the bottom, <9 volts, but voltage meter showed 13.6 at the battery while running. 12.25 when off, but auto headlights still on, and 12.42 when they turned off. Battery may be bad as I haven't had a load test done, but with the dash freaking out, I'm leaning more towards grounding issue.
AC is warm, steering controls do not work, lights on the dash were faintly flickering (high beam indicator) even when they weren't on. The headlights and all external lights work with no issues. Windows do not work now, and the interior light no longer comes on with the dash switch (stopped coming on when you open the door a few months ago, but still worked with the switch)
Also the Service 4x4 message is always there, I think it's a grounding issue with the diff, but I am not sure. The switch works and you can hear the transfer case changing gears. Putting it in 4 low does get you into low, but only the rear wheels engage. That has been like that for over a year though.
Any thoughts on where to start hunting the electrical gremlin? Battery test and cable check for sure, but after that...?