Twilight Zone horn works no fuse or relay

Hi! I just got my first car - a 2010 Prius I could afford at a salvage auction. Now I get to learn by fixing things! It's a GREAT car though! Only 40K miles, well-maintained, perfect interior, no airbags triggered, but it was hit from the front and somewhat repaired by someone before being auctioned. It is drivable!...but I have to pass inspection on lights, horn, and there may be some codes etc before I can register it.

Here's my biggest mystery so far: I took off the bumper to see the front damage, and noticed the horn wires had been violently pulled off. I figured they must have been blasting continuously and someone yanked them off. They literally broke the wire, so it must have been loud! I reconnected them, turned on power, and heard a small continuous tink-tink-tink sound from them. I've searched this forum, and one guy says that's just what happens with a damaged horn getting continuous power. Ok, so in the accident the horns got mashed, the wire to the horns got shorted to always give power. Find the short, replace the horns, all ok.

BUT....I tried pressing the horn button, and they work great!! Ok, so the horns are fine, but they're getting small power from a small short somewhere that makes them go tink-tink-tink continuously. Time to try to trace the circuit and see if I can find the short. To start, I think I'll find the horn FUSE and horn RELAY. I look in the fuse/relay box on the driver's side under the hood (I'm compressing this...in between, LOTS of reading and research on this forum and Google to get this far).

SURPRISE!!!! (Cue Twilight Zone music) The diagram on the back of the relay box cover shows where both the horn fuse and the horn relay are supposed to be. and.......THEY AREN'T THERE!!! So...now I have a horn circuit that WORKS and honks the horn just fine when I press the horn button in the steering wheel, has a continuous tink-tink at other times, and has NO horn FUSE and NO horn RELAY where the diagram says they should be.

????????huh????????

Can anyone out there unravel this mystery for me?
Thanks for any insight you can give!

 

I hadn't heard of that movie but I just Googled it and I think you might be onto something! The way she beeps and winks at me..I know she's trying to tell me something! And she has locked me out once already! Too bad I don't have a girlfriend to do further testing with!

Seriously, though, I had a friend look at it the fuse/relay diagram very, very carefully, matching all the surrounding fuses and relays etc...and he came up with the same zany conclusion. They're both (horn fuse and horn relay) just....... missing. I'll go out and see if I can grab a pic and post it here.

I hope someone will look at the pic and point out where I'm wrong. Is it possible the diagram on the cover is wrong and the fuse/relay are maybe combined with other fuses/relays??

I'm imagining someone who knew Priuses, after the accident, reached in and pulled the horn fuse, but that didn't stop the blaring, so they pulled the horn relay, and that didn't stop it, so they yanked the wires off. But then...how can the horn work when I reconnect the wires...?

 

uh oh....I'm already in over my head! What the heck does that mean? But yes..it has been fun and challenging. Nothing like working on a car you can't WAIT to get on the road in! But I've got to get rid of the tink-tink-tink or it'll never pass inspection. I don't mind that the horn mysteriously works without any fuse or relay, if I could just get rid of the continous tink problem, I guess. Just weird though

 

Here are the pics I promised, of the fuse/relay box cover and the actual fuse/relay box, showing where the diagram says the horn fuse and horn relay should be, and showing that they're not there. Please, someone, tell me I'm not seeing this right!

 

I've tested the lights and turn signals, because that was my first goal. A bunch of bulbs and even some sockets were missing from the accident...maybe taken out and thrown away? because the headlight unit was there, just no bulbs/sockets on driver's side. Anyway, I've replaced those and all are working now, on both sides.

The two reasons I know it's the horn are 1) as soon as I twist together the broken horn wire and turn on the power by hitting the power button twice, it starts with the tink-tink-tink sound, and 2) if I put my ear right up to the horn, it's definitely coming from there.

 

Mystery PARTIALLY SOLVED.
I found an Owner's Manual online and downloaded it. It has a diagram of fuses (though not relays -- I guess they don't want owners playing with relays, or something... The word "relay" isn't mentioned in the whole manual). The S-Horn FUSE is listed on the diagram, and next to it is the cryptic description "No Circuit". A search for "horn" in the fuse diagram shows the horn grouped in with low-beams and backup lights in a 40A fuse called P/I 2.

So...I'm guessing Toyota just put the Horn fuse slot in there for fun, but actually hid the horn circuit in with the low-beams (which makes sense I guess because the wire to the horns runs in the same harness as the wires to the headlights). AND I'm guessing there is NO HORN RELAY, maybe because with a 40A fuse & wiring, you don't need a relay????

Can anyone out there confirm that there is, in fact, NO HORN RELAY?? A lot of people have modded their horns, but most either add an inline relay or just hook the same wires up that went to the OEM horn, and never have to look for a relay. Does anyone know...IS THERE A HORN RELAY?

OK...now I'm down to the main problem: the horn goes tink-tink continuously. Actually, I just listened, and it's more like bluurgh-bluurgh, just like a horn that you apply low power to, not enough to fire it off fully, just to get a little blurgh out of. But where could that constant power be coming from??

 

Yeah, I'm currently believing that there is no dedicated fuse for the horn, it seems to be in with P/I 1 low-healdlights. And my current theory is that there is also no relay. Do you happen to know if that's true? I'm trying to trace the wires back, but sheeesh they're all bundled together and I hate to cut bundles apart to look for shorts. I'm just not really sure what to do at this point.

 

Definitely worth it! Glad to get a recommendation for them! I had seen they were available but hadn't know if they were any good, over my head, or not informative. I got a Haynes manual which my Dad said is great, but for the Prius 2010 (lumped in with 2004-2009) it was truly terrible. My Dad agreed, said they must have been bought out or going under or something. So, I'll try the download at the Toyota site...thanks!

 

Seems like you must be right. OK, I'll do that, along with a suggestion that just came in to download the electric circuits at techinfo at the toyota site. Maybe then I won't be totally blind.

But what do you think of my theory that there is no horn relay? Do you think that's even possible? I've googled it endlessly and have yet to find anyone definitively saying where the horn relay is on a gen3 Prius, so....I wonder?

 

Just found a Gen2 forum chat about the 10A fuse and horn relay in gen2. I'm betting the fuse/relay cover still has those marked from gen2, but for gen3 they did something else. It's all sorting out now, but where oh where is my short?

 

Thanks, AzWxGuy, for checking your panel. That's a big help to me...I'm going to stop worrying about the missing relay, which you confirmed must be a holdover from Gen2, and start checking the harness, along with ChapmanF's suggestion to download the circuit diagrams. I don't have a list of replacements, but I can see places that were damaged and I'll concentrate there. In fact, the violently disconnected horn wires might well have been from the accident, not from someone trying to stop horn blaring as I assumed. If so, that may be exactly where the problem is. Gotta do a school project first, though!

 

Yup, ChapmanF, you're exactly right. Why speculate when the answer is right there on techinfo? Btw, everytime I write the full URL, it stops me and won't let me post. In fact, I have to take the url out of your post in the quote above! How do you get away with writing the URL? Is there a setting somewhere? I gotta pause for a bit for a school project, but I SURE appreciate all the help and encouragement I've been given!