There are many threads about running wires through the firewall. The three most common approaches are (1) puncturing a hole in the grommet that takes the main wire loom into the vehicle on the driver's side, (2) drilling a hole in the firewall, or (3) cutting a nipple or two in the grommet that takes some cables in on the passenger side.
The first and second approach then usually bring up trying to re-waterproof with something like silicon, which isn't durable longer-term.
The thing all three of those have in common is they are basically not reversible without significant effort, if at all. So for someone like me that's trying not to do much to the truck that can't easily be undone, not ideal.
There is one hole through the firewall that appears in a few posts and which TRD_John has publicized on YouTube, which is a bit above and to the left of the main wiring bundle on the driver's side (looking from front of vehicle):
I used it to run the cable for my Switch Pros + a battery meter and, save a few knuckles that got cut fishing wires under the dash, it worked well. The best part is if you punch a hole in the plug for the wires (which I did) you can buy a replacement for ~$1 from Toyota and reverse the whole thing in about 10 seconds.
I'd like to run one more wire into the cabin to power some lights in the cargo area. And I'd like them connected to my fuse block ideally since I want to be able to have them on when camping and sleeping in the vehicle, so constant power.
I noticed a second rubber plug on the passenger side, but haven't been able to get a wire through the hole into the passenger footwell area successfully, although I can see where the wires on the bigger grommet below come through in that space.
Has anyone ever successfully used this hole for anything?
I figure that someone must have given in a whirl at some point, so before I start taking apart the passenger side of the interior to see what's possible, I'd ask the community ...