Fuel pump help needed!

Ill try to make this short. 2015 Peterbilt 389 Cummins ISX.
For many months when you turned the key it would go through the starting process but when you tried to start it nothing would happen. After many attempts it would start. I changed the ignition switch and PRESTO it fixed that problem.
It's been about 6 weeks and twice that same problem happened. Truck would not start. It doesn't turn over, just nothing. Try it again and it worked.
2 days ago another driver had it and stalled the truck climbing a hill in the landfill, no big deal but he couldn't get the truck started. They pull started him and he came home. In the yard he tried to start it again with no luck. Upon a closer look found the wire from the starter to the solenoid rotted/melted off. Not connected at all. By the looks of it, this has been bad for a long time. Im thinking it may be what caused the ignition switch to go bad.
Replaced starter. Now the truck would turn over but the fuel pump is not working. Normally I can hear it when you turn the key on.
I was thinking the damaged starter may somehow has damaged the ignition switch I had put in. So I just replaced that again. It did not help. The truck would only go "clunk" so I put the old one back in.
So the truck turns over again but now I have code J1939. My next step is to check for power at the fuel pump relay when I turn the key on to see if the switch is even activating the pump. But I doubt there's a problem since I already tried replacing the switch. So where do I look now. ??? I am also going to try powering the fuel pump directly to rule a bad pump out but I feel like the problem stems from the bad starter. I don't want to get tunnel vision on this and get hung up on the starter so I'm looking for others opinions.

UPDATE: Found there was no power going to the fuse box on the firewall in the engine compartment. So it looks like the starter was not hooked up properly, I'm guessing. They guy that put it in is not here and im by myself so any advice or pictures is appreciated.
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I just posted an update. Looks like your right. Is there a fuse anywhere before the fuse box on the firewall ? I have no power there at all.

SOLVED

I had no power at the Mega fuse but I did have power going to the disconnect switch before the Mega fuse. Undid the switch and looked it over and put it back together and EVERYTHING WORKS!!!
I had others helping last night. Apparently someone took it apart to check it and didn't put it back together right. So luckily it turned out to be a simple fix for a big problem.

 

You were definitely on the right track. Disconnect switch before mega fuse and been taken apart and not put back together properly. I appreciate your help. Im horrible at electrical stuff so I was getting nervous.