Why is it that Toyota insists upon keeping so many SIMPLE things such a big secret?! I have searched for nearly an hour here and online for the location of the horn relay ( NOT the FUSE!!!) for our 2012 Highlander. Should be no big deal! The fuse (which is what ALL internet searched provide the location for despite searching specifically for the relay) is ok. It has to be the relay. Was trying to upgrade to a decent horn, (as I see now MANY owners do!) but when I tried it out, it worked one time then the whole thing quit... No High, no Low, just dead...
Southern
You can't find one because there isn't a user accessible one. None of the external relay's in the engine block electrical box are for the horn. Its built into the "Engine Room Junction Block Assembly" that's part of the electrical box out there. The low beam relay and high beam mosfets are also built into it. I'm under the impression its not user repairable if you fried it, though I've never looked at it directly.
Red box in the picture attached is the module. Its plugs are on the bottom (~4-5" deep), the ring terminal is the main 12V supply that feeds all the circuits it powers. High and low horns are wired in parallel, hit the fuse, and then the relay. The fuse should have protected the relay (unless you replaced it with a higher amperage before this..). Remove the fuse, use a multimeter and stick it the fuse slot. Check for voltage on one of the fuse socket legs while someone else is hitting the horn. That'll let you know if its the relay or not without digging into things further. Also check for continuity between 1 of the socket legs and the + wire of the horn plugs. If neither give continuity, you've damaged the wiring between the modules plug and the horn plug.
Red box in the picture attached is the module. Its plugs are on the bottom (~4-5" deep), the ring terminal is the main 12V supply that feeds all the circuits it powers. High and low horns are wired in parallel, hit the fuse, and then the relay. The fuse should have protected the relay (unless you replaced it with a higher amperage before this..). Remove the fuse, use a multimeter and stick it the fuse slot. Check for voltage on one of the fuse socket legs while someone else is hitting the horn. That'll let you know if its the relay or not without digging into things further. Also check for continuity between 1 of the socket legs and the + wire of the horn plugs. If neither give continuity, you've damaged the wiring between the modules plug and the horn plug.
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