Would appreciate help for a Toyota Corolla 2007 non-working horn.

Did you have to remove the clock spring? If so makes sure you did crack it when reinstalling.

a blessing.. really.
the parts guy is just a clerk, he dont know what is wrong or how to test anything, or he'd be in the shop making cash.
so if 12vdc reaches the horn, (a $10 walfart meter works)
the horn is bad. or that rusty ground on the horn is rusty. ...
rust don't conduct, current. at these levels...
buy a meter and do that check
DMM to 20v range.
set to volts.
black probe to body (metal)
red probe to horn wire. (hot wire when active)
got 12v, , yes, then the horn is bad, or not grounded.

look for ground problems ,replacement horns can be had for 10.00
at most auto parts stores.

You can replace the horn. Check to see if the wires connected to the horn have power. Check with a test light. If power is present then the horns are bad.

their is a secondary fuse for the horn/ hazard like circuit in the engine bay, front left hand side. i think from memory it is a 20amp blade fuse

Try checking for a bad or broken connection or a blown fuse.

2003 corolla, horn stop working and now air bag light is on. Was told a senor was out on the steering.

Dear Mr. bclester, you have not indicated whether you have checked your fuses. First check them and then if they are ok, check the horns themselves. Remove them individually and test them on your battery. Are they fine? Let me know so that I can advise you on what to do next.
arturocruz

check fuse then check relay or just check for power on the horn it self

the horn is located behind the bumper, you will need a test light to test for voltage at teh horn connections, if there is 12 volts at horn connections, this means th horn is faulty.
if the horn is okay, check the horn relay - and if that is okay it could be the horn pad inside the car.
But it will most likely be the horn itself that is faulty.
Ask your local garage / mechanic if you are lost!!!