What I've been reading for years on this and other RV forums is that modern RV diesels don't use glow plugs...the gensets do, but not the engine. A heat grid though...actually, don't recall hearing about that device, so failure must be pretty rare. Doubt I have one of those on my engine as I can't see any wires going to the turbo, before the turbo, or anywhere around the intake manifold. Something I guess I don't have to worry about.
Many of these rigs have relays in the BCC (Battery Control Center), along with some fuses. Have you checked in there for a blown fuse? Or for relays?
Did the rig come with a Cummins book? Or the chassis book?
(I'm surprised no one else has jumped in here with some expert advice).