YOUR horn notwithstanding, it's usually a pretty fair indicator of how much current a particular circuit uses. If it weren't, they'd just use 30A fuses for everything and avoid any possible confusion. You're also assuming that nothing else is powered off the same circuit as your horn. Just because there's nothing else labeled on it doesn't mean there's nothing else drawing power through it.

It's also running the brake lights :p which aren't huge electricity-suckers either :D

If, as you suggest, fuse amperages always corresponded to power draw, you'd have 8 different fuses in every car.

Since most manufacturers realize that that would be retarded, they slap in 3-4 different kinds, so you can carry spares, etc.

This means, that some will have circuits which will not have the PERFECTLY corresponding amperage fuses. Which brings me back to my original point, that you can't judge how much power something draws in a vehicle by simply looking at fuse amperage.

I didn't say it would be an EXACT indicator, did I? I said "pretty fair indicator". Something that the automaker feels requires a 15A fuse is probably gonna draw - or could be capable of drawing if everything is active - more than 10A, or they'd have just put a 10A fuse in there.

I wonder if my horn/brake lights need more than 10A...something tells me they don't...

Still...this is getting pretty petty...so I'm ready to drop it if you are haha

Noooooo....... Fight fight fight.....

:Popcorn

The horn is on for maybe 1 sec, it's not going to use much. On the other hand, defrost, heater fan, lights, etc are constantly drawing power when it's turned on, and that puts load on the alternator, which puts load on the engine. It's not going to draw max amp the fuse is capable of handling, but it's going to be constantly drawing power, where as the horn doesn't.