Shuts down in rain

i have 1 time a similar problem ,water was going to the fusebox{only when was raining}

 

Check your windshield gasket. Cascadia has a lot of complaints about water leaking around the windshield. Then it soaks the electrical connections and fuse boxes mounted motor side of the firewall.
Check the truck clearance lights for leaks also.

 

The cab marker lights above the windshield. The gaskets or caulk might allow water to leak inside.

 

Also make sure you do not have any holes on your front cowl, this is right under your wipers. Also make sure you have the hoses attached to cowl that divert the water from your electrical/fuse area.

 

Proper fix is to have the windshield removed, reinstalled and resealed properly, this still happens with every Daimer truck I buy.

 

Have you tried to get a code when it shuts down?