under the hood, on the firewall, there are plastic, rubber, or metal plugs
Pick a plug near where you want to run your wire to keep everything looking the way that you want it
Check the opposite side to make sure there is nothing in the way of drilling & running the wire through.
Then a bit of silicone will make the hole water tight
I'm sure that someone will post a pix of what they did to their own Ram
I ran a wire from my battery to a small fuse box that was firewall mounted & a wire from it through the firewall & to my CB radio, my radio pulls 50 Watts, 18 AMPs
There is a rubber grommet where the main harness comes from the TIPM (fusebox), through the Firewall. Just underneath the large bundle of wires is a small rubber nipple that is made for running wires additional wiring through. Just cut the tip off. Its about a 1/4" hole so most wires will fit. Silicone once everything is buttoned up.