No Accessory Power With Key Off

2021 Pete 389 day cab.
Truck operated just fine up until I parked it last Friday. It sat for 2 days, untouched. Got in this morning, I notice the interior lights didn't come on when I opened the driver's door. 1st impression was the batteries must be dead. I turned the key ON, the dash lights up and interior lights all come on. Truck cranks and runs fine. I noticed the dash clock was reset to 1200. I did a pre-trip and all is good. I reset the clock and headed out.

Drove it 13 miles to my loading point. Turn off truck. After it sits about 10-20 seconds with the key OFF, the cab loses all power. No interior lights, no headlights, no hazard lights, no dash instrument lights coming on when the doors open and clock defaults to 1200. Same as it was when I got in this morning. I turn the key ON, everything energizes, all interior/instrument lights come right on and it fires right up...zero hesitation or starter drag. I pulled the battery box/steps and checked every battery terminal...nothing loose, though I snugged up each one a little tighter than they were. No corrosion present. Edit: The 12V power outlets DO have power when nothing else does.

This scenario continues all day. I checked every fuse under the dash and also under the hood (that I can find). Nothing obvious is jumping out at me. I have not crawled under to check the starter connections...yet. Any suggestions?

 

Wouldn't that cause the LVD message to appear on the driver information display?

 

No Smart Air system.

Today, I load tested each (x3) battery to rule them out. They all tested at 12.6 volts...which is perfect. I've been trying to locate the LVD relay/fuse to test it, but I don't have any idea where to find it. I read that it would likely be under the sleeper box on a sleeper truck, but mine is a day cab.

Inside the battery box there is a master/main fuse, which tests good (power on both ends). There is also a breaker that can be manually tripped and reset. It seems fine too. There is another big fuse on the firewall by itself that checks out with power on both sides. I'm not sure what it is because it's not labeled. It has a LOT of dielectric grease inside it.

I guess I can call my local Pete dealership and see if they'll tell me where to look for the LVD relay. They usually say, "you'll have to bring it in" by default.

 

It does have it. Several months ago, the LVD icon came up on the display screen due a weak battery (interior light stayed on all weekend). I recharged all the batteries and the light icon went away. Strange part is, it wasn't cutting the power to the cab accessories when the icon was showing like it is now. I'm just puzzled since it's giving all the symptoms of a LVD activation, but no icon on the display coming on. Haven't called the local Pete dealer yet. Probably will tomorrow.