Electronics restarting while driving.

Loose something.......
Probably a main earth lead, but could also be loose B+...
Check all the connections from battery to block, chassis, and starter motor.
I doubt that they messed with the fuse box, but checking the 3 heavy brown wires on the bottom would not be a bad idea.
They may have omitted completely the cable from the engine block to chassis, so have a look.
If a connection looks OK it may still be loose or corroded, so loosen, clean if needed and re tighten anything you find.

Ahhhhhh......
It really helps if you let us know ALL of the things you did, otherwise we are tossing hand grenades in the dark:razz:
Sound's like possibly one of the plugs on the bottom of the fuse box is not seated or, as mentioned, one of the main B+ leads underneath is not properly tightened....
You said "Was Replaced"? Does this mean with a brand new fuse box, or a used one??
The under bonnet fuse boxes on these rigs are getting long in the tooth and will cause any number of odd faults. Also, if the mechanics replaced the fuse box, did they replace all the relays as well?
Could be a bad relay causing this.
What was the reason for replacing the fuse box in the first place? Was the main board burnt? the relays bases burnt? was one of the plugs on the bottom corroded? all of them corroded?
Plugging a corroded plug into a new fuse box will cause issues as will re using a dodgy relay......Easy fault to miss too.

annette said:

last but not least is the B+ on the fuse box on top well connected..I made that mistake once

Click to expand...

+1 on that one as well!

So....Yes, check BOTH ends of the main B+ lead:dance:
And, of course, the notorious single bolt wedge OEM battery terminals, which when fully tightened can still be a loose slip fit on the posts