I ran my cables for my laser jammers along the right side of the engine compartment and into the cab. Pop the cover the the electronic box, pull the large black rubber boot out from where water drains trough but leaves don't, you'll see a silver dollar sized black rubber bun with a large wire (loom maybe) coming through the middle of it. I poked a hole through that, pushed my 24" long flexible booger-picker type tool through the hole and into the cab. Went into the car with a flash light an looked around until I found my tool poking through.
Only thing to watch out for is pulling the leaf guard thing off. There are two plugs that help secure it. The tough one is low, against the firewall, and more towards the center of the car.
'15 3500 HD Dually