There is a BIG difference between spending 20.00 on a horn or thousands for a car on Ebay.
If the seller is reputable he will stand behind the horn to work. Not sure that comparison holds water.

In this area you would play hell trying to find a correct set of horns in a boneyard for a classic mustang.
You might find something to physically fit, but more likely than not they wouldn't be correct.

 

Are you sure your horn is totally dead? I just went thru the same experience with my horns that didn't work on my 66 stangand found out that the 2 contact brushes inside the horn ring needed replacing and after that found that one of my horns was not properly grounded to the body. They work fine now

 

Yeah, I wouldn't buy a car off Ebay, but I also stated I have bought and sold a lot of low dollar items off Ebay. You are not going to find a classic mustang in a bone yard to get the horns off it. Forget it, you will just be wasting gas.
Take the horn out and ground it real good then hit it was a wire from the battery and see if it honks. 5 bux says it still works.

 

There are a couple of used Mustang parts sources that are close by where I live, well if you call an 80 mile one way trip close - Mustangs Plus in Stockton, and they do have used parts. Most Mustang shops have an inventory of used parts, horns included, and you need to check them out. I agree, looking for parts in a generic junk yard is a waste of time (except for engines and transmissions).
Jim

 

to me with ebay dont spend more then your willing to lose things can get damaged in shipping or seller could just rip you off