Suggestion on where to run electrical power wire through the firewall into interior?

[Lumberjack]

I am running a 12 gauge power wire from battery into the interior of my 2012 Mazda 3 GT to hook up a trailer wiring harness in rear of car. I did a look today and there doesn't appear to be anywhere easy to pull the wire through on either side. The drivers side appears to have a harness coming through as I can see it from the inside of the the firewall but it doesn't appear to be accessible from the top of the engine compartment. There is allot of empty space on the passenger side engine compartment but I don't see anywhere to route a wire through. Can anyone suggest a place that I could run this single wire through?

If anyone questions why I am running a power wire from the battery for trailer wiring harness? I am using a module that isolates the trailer wiring from the cars electrical system and it powers the trailer from the battery (not the cars lighting system). I have used one on my bike and I love the fact that it see the load and not the cars electrical system. Especially since I have two sets of lights on my trailer and in the past I have had to change the flasher relay in my previous cars since it is a bigger load.


Thanks

[peterm15]

So basically you have to run it like an amp wire?

There is a bunch of wires that go the passenger side ( at least in gen 1, I think I read it's the same with gen 2)
When hooking up my amp I pushed the wire through there. It comes out being the glove box. I ran 2 gauge so 12 shouldn't be an issue.

[Genpu_Mz3]

if you look on the passenger side firewall under the hood, you will see 2 stainless lines going through the fire wall with a rubber gromet. you can put it through there. i did with my amp power wire.

if not take your battery box out and run it with the main power harness, just take a wire hanger straighten it out cut off the hook end, file a point on one end, then tape the wire to the sharp end of the hanger, spray some wd40 on it for lube, and poke it through that gromet.