After sitting in the snow for a couple weeks, the second horn (in front of firewall on passenger side) starting blowing by itself. At first a little distorted, like a connection was not solid, then after moving the car, it started at full blast. The noise stops when the key is in the run position, but when the key is in the stop position, the horn starts again. The primary horn (above radiator) is not affected. The horn button on the steering wheel still works normally, and makes a solid connection to operate the primary horn, whether the secondary is hooked up or not. So, I removed the wire from the secondary horn, and the noise stopped, of course.

I do not think the problem is in the secondary horn itself, as it can only blow if it is getting power, and it should not be getting power when the horn button is not depressed. I also do not believe it is the alarm, as it would be trying to fire both horns, not just the secondary. I tested this by pressing the panic button on the fob with the secondary horn disconnected, and the primary horn still blew.

I see that each horn is on its own fuse circuit, but I can't figure out how to remove the 7.5 Amp fuse for the secondary horn. Perhaps it is a horn relay for the secondary horn, but not sure where that is (under dashboard?, and how can I identify it). The owners manual doesn't even provide a fuse map. You have to read the cryptic letters inside the fuse box lid under the hood.

I am tempted to wire the primary and secondary horns to the same circuit, bypassing the secondary circuit, but I am concerned that the amperage would be too high. The primary uses a 10 A fuse, and the secondary a 7.5 A fuse.

Any ideas would be appreciated.

 

I don't have the diagram for the 07 but I am sure there is at least one horn relay. No way they would run full horn current through the wheel contacts. If the return spring inside the relay fails, a jolt or even temp change may cause the contacts to make a flakey connection. Is it an aftermarket alarm? Have you had any body work done?

 

I really appreciate the response. The car has had no bodywork, and the alarm is the factory original. It is true that the car had been sitting with 2 feet of snow on top of it a few days prior to the horn incident. It could be some ice causing a short somewhere. I brought the car into the garage, which is only slightly above freezing temperature, but is allowing some snow which blew up under the car to melt.

The strange thing is that as soon as the key is turned to the run position, the second horn stops blowing. The primary horn is not affected at all, so probably has its own relay.

Thanks again.

 

It sounds like it may be a horn for the alarm only. It is true that cars used to have two horns and the "beat note" between the two made the sound more "annoying" (which is the idea) but many cars now use a "electronic horn" which is driven by a "horn tone generator" chip and the horn itself is just a speaker. (lighter, cheaper) Any chance you can compare your car with another '10 to see what horn works when? The alarm horn is often mounted in a place where the morons can't get to it easily and yank the wire before breaking in.

 

Hi: Very interesting. I am used to old American iron, where there are always two mechanical horns, and in some cases (old Caddies and a Buick Riviera) three horns.

Although with the second horn disconnected, the primary horn still blasts when the panic key is depressed on the fob, it would make sense that for the purpose of the alarm, both horns would fire, to make the car as loud as possible.

Your answer is also logical in that the secondary horn is difficult to reach to make it harder to cut the wire, and that it stops firing when the key is turned to the run position.

Thank you for your intelligent response. I really appreciate it.

Brian

 

You could pull the alarm system fuse and see what happens. Otherwise you really need the factory circuit diagram to figure out what interconnections there might be. I always apporach things that worked right - once- differently than those which never worked properly.

 

Hi: Is there a special tool to remove the fuses? They are nearly flush with the panel. Never seen fuses like this before. Thanks again.

 

Toyota used to put a little white tweezer in one of the fuse boxes, otherwise a pair of long nose pliers perhaps wrapped with black tape to be easier on the fuse is in order. NOT cutting to the chase, I use a product called "DeOxit", a professional grade contact cleaner and lubricant (Radio Shack actually sells it to my surprize, perhaps because it really works) on the fuse blades, improves the connection and makes it easier to get out. It does help, as you have seen there is not much grabbing room. You might want to Google "Caig Labs" The Shack may have the "felt pen" type applicator which is all you need. If you ever had a "pull out" car stereo with a bunch of contacts on the back which mated with a connector in the dash, this was the stuff which kept them working. HP, Tektronics, and other high end companies refer to it by name in their service info.

 

Good news. After thawing out for a few days in the garage, I hooked up the alarm horn, and it did not start to blow by itself. Perhaps it was some ice/moisture that reached a wire harness or some other place it shouldn't have (due to the 5 feet of snowfall we had while the car was parked outside), and now that it has melted away, we're good to go (hopefully). Thanks for all your help. I learned some helpful info that will be useful in the future, too.

 

Looks like the problem is narrowed down to the alarm. Alarm design is not rocket science, but there are some tricks. In order for most alarms to stay OFF, the switches on doors, hood, and so forth must be closed and conduct a very small current. It is the opposite of the switches which turn on the dome light, they open when the door is closed to shut off the light. A thief who clips an alarm switch wire does not disable that part of the alarm but rather turns it ON. Bad for him If one of your switches got some water or ice in it, it might not make good enough contact to "signal OK" to the alarm. You should check all your switches and perhaps spray a little WD 40 on the pins. DeOxit would be better, but.... The hood switch and the door switches are often exposed to the weather so look at them closely.