I'm trying to install a small ham radio in my 2014 Mazda 3 hatchback. I've worked out everything but the power. The radio manual says that I shouldn't connect the radio to the 12V in the cabin, because when you transmit, the radio draws lots of current and the circuitry can't handle it. They supplied their own cable, with inline fuses (fastblow) so you won't burn down the car.

The thing is, I can't figure out how to get the cable from the cabin, through the barrier, into the engine compartment and thus to the battery. Surely there's a wiring harness somewhere that I could slide the cable through (it's not really that big).

Does anyone know how to do this?

Thanks.