I know this isn’t through the firewall BUT…
If you are thinking about drilling a hole, (which I thk is a good idea) think about running the wire under the cab, tucked away so it doesn’t get caught on anything.
Drill a hole on the rear of the cab and use a water tight connector, maybe even run the wire up through the floor.
I ran my Amateur Radio Power through the rear of the cab and never had a problem with interference with any electronics in the cab.
Just me thk’g out loud.
4x4, 5sp, Std Cab, Stepside, E4 Red
4” Lift - Coil-Overs, 6” SkyJacker Leafs - No Blocks (Mistake)
31 Spline FX4 Rear Axle, 4.56s and OX Locker, Hurst Shifter w/Optional Stick and "Made by Grev" alignment adapter