FLC 120 no crank, new batteries, starter, solenoid

I remember now. Ugly MF'ers.

On the right side of the fuse box, there's a red cover. Any mega fuses over there?

 

Ssee my post above about the megafuses.

Also, check that ignition switch for grounds, and you can just use a screwdriver to jump it like you did the starter. Just don't jump it to the ground. All other posts on it are accy, on, or signal

 

I would get my Freightliner parts person to E mail a diagram of that circuit to me.
Without a power probe frequency tool I would often unhook the positive battery wires. Vise grip a fuse to the battery terminal. Connect a jumper wire to that and the wire I want to chase. Then it will be the only wire hot in the whole truck. I thank it goes from the switch through one of three big firewall connectors under the air filter to the solenoid. I would start there. But maybe it goes through the fuse - breaker panel?

 

It was a freightliner classic but used to have a big fuse in battery box. It went inline to the computer, same year model, maybe the century had one as well.
I say big fuse as not a mini fuse, it was like a 30

 

Top right, orange and blue. Ditch whatever that tool is and go grab a test light. Those 4 studs on tbe right should also have power with key on IIRC.

Step one would be get a test light tbough