Who told you that......and why do they think that is the problem ? It is more likely that: The horn itself has failed OR One of the wires to it is loose or broken.
I don't know if it's necessarily more likely ... spiral cables are known to wear out. One of the wires to it ... broken ... could certainly be one of the only wires in the car that get wrapped back and forth every time you steer. So it all boils down to the first question: yeah, what was the evidence they relied on to tell you the spiral cable is the problem?
Car horns are cheap and unreliable. THEY are known to "wear out" at a much higher rate. Especially if they happen to be mounted where they are exposed to "road spray". The point IS.....which I failed to explain.....that testing the horn itself should be a fairly quick and easy process and you should do that first. And while you are there, inspect the connections.
Known by whom? Extrapolating from my own experience would lead to the conclusion that car horns are eternal and should be used to build intergalactic spacecraft. Come to think of it, I did have to tweak the adjusting screw on the back of one once, back around 1979. There might be good large-sample comparative data on horn vs. spiral-cable failure rates somewhere; if you know of some it would be interesting to see. A lazier approach might be to search PriusChat some, but my casual impression is that would turn up more spiral cables than failed horns. In any case, the OP in this thread is probably only slightly interested in large-sample comparative statistics, and much more interested in why one particular horn isn't working, and that's the kind of question that's answered faster by grabbing a meter and seeing why it isn't working. Or asking the person who said "it's the spiral cable" why they said that.
Usually when the spiral cable goes, you lose the functions of more of the steering wheel buttons. Check the functions of all of those, and if anything else is out I would put all of my money (literally) on a failed spiral cable. I would have dropped some of the engine covers already, in the front of the vehicle, and checked the horn connection to the vehicle wiring harness, and probably a continuity test of the horn itself.
Aside to enterprising PriusChatters: if you have access to a Prius that happens by coincidence to have more than one problem with horn and HVAC or AV or cruise controls, there might be some money to be made here.
A continuity test isn't good enough. The thing that most often fails is the contacts on the "vibrator" switch. And for the record, over more than 50 years, I've owned maybe 40 different cars, trucks and motorcycles. I have NEVER had a "spiral cable" (known by several different names) go bad. Not ONE. I have, however, had about 4 horns go out. One was wiring. The others failed electrically. One should ALWAYS test the easiest and cheapest thing first. (Are you SURE it is plugged in......and that the outlet has power ??)
Only the most recent two cars I have owned have even had spiral cables, so all the years before that, I wasn't ever seeing a spiral cable wear out because there wasn't one. (Even my '84 Bronco II, which had wheel-mounted cruise buttons, didn't use a spiral cable, just a commutator with brushes.) Every Prius, on the other hand, does have a spiral cable. The coming of airbags seems to account for the change; nobody wanted to trust a brush commutator for setting off the bomb in your steering wheel.
To find out if it is your "spiral cable"/"clock spring" Do any of the buttons on your steering wheel not work? How about your airbag light, does it stay on or come on/off when it wants? Then your problem is the "spiral cable". I just replaced mine last week and all issues are fixed though my horn was still working at the time but so were some of my steering buttons but not my trip or disp buttons. Posted via the PriusChat mobile app.
Another easy check is to hold down the horn button while you turn the wheel back and forth. If the horn is repeatably honking and unhonking as the wheel turns past particular spots ... spiral cable for the win. The spiral cable is made of several separate conductors that won't all fail at the same time, so a check like this lets you diagnose as soon as one thing goes flaky without having to wait until the horn / AC / radio / etc. have all joined in. Of course you can do the same check more or less no matter which thing goes flaky first. If it's your AC temp button, hold that down and turn the wheel, and so on. It's easy if your problem is horn because you can hear it; makes for a pretty convincing test.
I just wanted to thank ChapmanF, sam spade 2 and Azusa for an informative and entertaining thread. Laughing so much, it's easy to forget that I'm learning a few things here. Now, about those intergalactic spacecraft ... , wondering if I could get some seed money for the R+D based on some clever wagers with AzWxGuy ...
