1999 Peterbilt 379

Check the ignition wiring in the dash.

 

Ignition relays behind the left dash panel. Simple to check with a test light

 

You need to ck all of the wires for rub tru places from ECM to where it gets power from?

 

Have you tried a diagnostic with the cruise control for any codes?

 

2015 Volvo this exact thing happened to me, no code just everything went dark then come back on. Or I pull over, turn key off and restart. Random, 6x's one day, then fine for a week, then 2x. I pulled the ECM had it tested, no problem. Replaced the big ground fusible link wire to the frame. Replaced the battery cut off switch, Cleaned the battery connections, installed new bus bars, new positive cable 250a fuse, pulled all the connections off the firewall and cleaned them, basically anywhere I could find a ground, removed, cleaned and re-installed. Just got back from 8-day run and she ran perfectly.
In my opinion it has to be a ground or wire rub through that is temporarily zapping the system is the only explanation I can come up with Good luck

 

I had this exact problem on my 99 pete. It happened three separate times to me. The first time it was a corroded connection for the wire coming off the starter. When I went over a bridge joint the truck would just off, 1 second later it would come back on and run like nothing happened.

The second time it was corroded battery terminals.
And the third time was a corroded/ broken wire coming off one of the batteries. Im still not sure what that wire went to but it caused the same problem.
My truck spent its life near the water and hauling salt in the winter so im constantly finding corrosion.