do i need a relay?

Hello! I've been lurking on this website for quite a while now and I must say that the information here is the best on the web, and the people here are true gurus of electronics. Happy to be a part of this forum.

I can usually find the answers I need by searching around, but this time I struck out. So, I decided to join and ask the experts for help.

I have a 1982 Chevy S-10 pickup. It has a single horn on it and getting people's attention in traffic can be difficult. I want to add more horns to it, but I'm not sure if I can do this without adding a relay. I went to the junkyard today and I got a four horn set-up off of a Cadillac. I forgot to check the vin tag to get the year, but I think it was about a 1987. I checked the vehicle chart here at the 12 volt, and it turns out that both my S-10 and the Caddy have a negative horn switch. Also, the horn on my truck just has one bolt holding it down, and one terminal on it. This is what I looked for on Cadillac horns, and the horns I bought are the same.

Now, I've tried to do this on another truck before (a '79 Chevy C-10), and I couldn't get the horns to work. Before I make a bracket to mount all these horns and get them installed I'd like to know what I need to do to pull this off.

If I do need a relay, a schematic telling me which wires go where is greatly appreciated. Thanks in advance for the help!     E

There is already a relay powering the original horn.  The only problem may be the wire size feeding the horn.  Just to make sure that is not an issue, wire the relay as follows.  Terminal 30 to the battery via a 12 Ga, wire and 15 amp fuse at the battery.  Terminal 87 connects to the new horns.  Terminal 85 should be grounded.  The original horn wire should connect to terminal 86 and still be connected to the OEM horn.