Brake light fuse blows?

It is still a short, but an intermittent one. Two good suspects are a trailer wiring harness that is chewed up, and stuff rolling around in the trunk that has damaged the wires.

A simple trick to finding a short is to replace the blown fuse with a pair of spade terminals, then use small jumper wires to connect them to a twelve volt light bulb. A brake light bulb works well. When the circuit is live and the short is present, the bulb will be full brightness and hot so be sure it is not laying on the carpet or against a plastic door panel. Now you can unplug electrical connectors and move things around to see what makes the short go away. When it does, the bulb will get dim or go out.

For intermittent problems like yours the bulb may be dim already. Watch what takes place when it gets bright. That is when the short is occurring. It could be due to the rocking of the engine when you shift between reverse and drive. It could be due to the body flexing when you drive over bumps in the road. The bulb limits current to a safe value when the short occurs, in this case about one amp. You can use a stick from the seat to hold the brake pedal down about an inch to turn on the brake lights while you are troubleshooting, or you can remove the brake light switch from its holder so it will stay turned on.

You do not even have to watch the test bulb. When you move something that makes the short occur, the rear brake lights will go from dim to fully off.

My guess is the computer flashes the brake lights, and that is how the two systems are tied together. This is where using my test bulb in place of the fuse is so valuable. Watch how bright the bulb gets when you lock and unlock the doors with the remote.

It sounds like this is all related to the remote entry system. Intermittent problems can be very difficult to find, but a common cause is a failure of the computer module, and on some car models, they are prone to water leaking into them, either from a leaking windshield, plugged AC condensate drain tube, or just from excessive humidity in the air. Problems with this system usually end up being a dealer item.

"Dealer item" means the dealer's service department. There are a lot of things designed in to make it really difficult for the people at independent repair shops to work on today's cars. A few manufacturers go way overboard in that regard. They're protecting the profits of their dealers at the expense of their customers. This doesn't apply to Honda as much as it does to a few other manufacturers, but when it comes to anti-theft systems, remote-keyless-entry systems, and some proprietary designs, they aren't happy about divulging the service information or making required equipment available. If any mechanic could work on anti-theft systems, for example, so could the car thieves, so those systems would only be effective at keeping owners from driving their cars. We read about that much too often already.

Also, most independent mechanics have to relearn every system on every model every few years, and it's impossible to keep up with all of it. Doctors only have to learn two models in varying sizes for their entire careers. More experienced mechanics typically specialize in a few areas, just like doctors do. You'll find more of those specialists at new-car dealerships, and they continually get factory training on the latest systems. They have also seen your car many times, and often know right where to look for problems. Sometimes they already know what's wrong when they're still driving the car into the shop. But remember too they usually only see cars that are still in warranty, or are up to five years old. It's the independent mechanics who get to see what happens when those cars are rusty or have been driven in salt, snow, and water for many years. The dealership also has the advantage of having a help line they can call. Some of them have really good people. When I could reach the head of Chrysler training for all of Wisconsin, she almost always knew the answer right away. Part of her job, when she wasn't teaching classes, was to diagnose cars with problems, and develop the procedures that would show up in diagnostic manuals later. When you called the help line, you worked with the same person over multiple calls until the problem was solved. Some help lines are staffed with people who simply read from a script, and if you have to call back, you get a new person who starts all over from the beginning. I don't know where Honda fits on that scale, but at least the dealership mechanics do have resources not available to the independent shops.

Yeah, I would have figured that out, ... Eventually!

Actually, this is a perfect example of where the symptoms don't point to an obvious cause, but your mechanic had the experience to know right where to start looking. Sometimes a circuit is powered through a fuse for a totally different circuit because you will notice that second circuit isn't working. In this case, the horn fuse could blow, then you'd never know it until you needed it in an emergency, and it didn't work. Then it would be too late. Chrysler used to do that with their rear wipers. They tied that in with the Air Bag system. If the rear wiper motor shorted, you'd never know that either, except it blew one of the two Air Bag Computer fuses, and that turned on the "Air Bag" warning light, and that got your attention. Happy to hear it's solved.