To keep it simple, YES, it is that easy.
Your radio should have come with a power cord. If it didn't, get one that is correct for your radio.
The hardest part is routing the cable from the inside of the vehicle to the battery. Some vehicles it is very easy, some not so much. You can usually pop the hood and start looking around on the firewall (behind the engine) there will often be a number of feed through points on the fire wall where wiring and control cables will pass through. If you can find one of these, you can sometimes sneak the wire through there. Others, you may need to make a very careful incision on the rubber seal and run the wire through there. It won't be super easy, but it isn't rocket science. Just go slow, double check everything and get some help if you need it.
Best thing to do is work in a well lit garage. Pop the hood on your 4 runner and start looking. When you find a likely area, check on the inside under the dash board. If you can see both ends of the feed through, you are in good shape. If you can't, it's going to take some work. Often you can use a piece of coat hanger that has been bent over on the end as a probe. Make sure there are no sharp points on it, so you don't damage anything. You can use that to fish the wire through.
If you absolutely cannot find an existing place to route your wiring through, you may need to drill. This might be the point where you'd want to get a shop to do it. Even some stereo and alarm shops could likely handle this. You can certainly do it yourself, just make sure you know whats on both sides before you start drilling.
What you REALLY need to be careful of is how you route the wire. If you pass through the firewall, you MUST use a rubber grommet of some type. If you don't, the wire insulation can get worn away on the sharp edge of the hole and you will have a short circuit from the positive lead to ground. If you are lucky, this will just blow the fuse. If you are not lucky, you can start a fire. Also, NEVER run power wiring through the door. Never.
Once you have the cable run, route the inside portion to your radio. Be careful in how you route it. Don't run it under carpeting, or anywhere it can get pinched or damaged. If you need to, use ty-wraps to secure the wiring under the dash board and up to the radio. If the wiring is exposed anywhere, use some split loom tubing to cover it up. It protects it and makes it look nice. Once that part it done, move to the engine compartment. Route the wire to the battery location being very careful not to get the wires near anything that gets hot, or moves. Be careful around hood hinges also. Use the split loom tubing to cover and protect the wiring under the hood. Once you have the wire at the battery, you are just about ready to go. Make sure the radio is unplugged and you pull the fuse out of the holder on the radio power lead. Connect the RED wire to the positive post on the battery. Use a good crimp on connector that is designed for the task. The fuse holder should be close to this connection point, within 6 to 12 inches is good. You want the fuse close to the source to protect the wiring run. If you put it too far away from the battery, any damage to the wiring between the battery and the fuse will likely cause a fire.
The black lead should be connected to a body ground. You should be able to find an existing wiring ground point near the battery. If you can't find one, you can use a self tapping sheet metal screw with a star type washer. Drill a hole smaller than the screw. You will want the star washer between the wiring connector and the sheet metal. Tighten down the screw to secure everything.
When you are done, double check everything, make sure it's all secure and not going to get damaged by any moving or hot parts. If you can, use a multi meter to check for short circuits on the positive lead by doing a continuity check from the radio end to a good ground inside the cab. If there isn't an issue, you can go ahead and insert the fuse on the radio power lead near the battery. Go back inside the cab and confirm you have 12 volts (you may actually see something between 12.5 volts and 13.8 or so) Make sure the positive is really positive and the negative is really negative. If you are confident it's correct, go ahead and hook up the radio. Always hook up your antenna first. Then hook up your power. It should power up. If it doesn't, go back and check all your connections. Check the fuse and make sure it is OK.
You ain't done yet!
Every now and then, check the battery connection and the grounding point. If there is ANY sign of corrosion, clean it. If it is loose, fix it. Keep a close eye open for any damage to the wire. Do the same with your antenna lead. If you are using a permanent mount antenna, periodically pull the antenna off and check the mount. I have seen a lot of neglected antenna mounts in my day, and they can cause all kinds of problems.
Take pride in a job well done!
