I'm trying to set up another horn in my car, and I have

Terminal 30 should go where ever it's easiest to get voltage. But, I would find a switched fuse block not being used. Either you have a second switch or have a 3 way switch so you can use your steering wheel's default horn location.

File: 1453169292536.jpg (22KB, 400x300px) Image search: [Google]

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?

File: 1303449668058.png (361KB, 499x357px) Image search: [Google]

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>>932493
You'll need a switch between either ground or 12v that chooses either old horn or new horn. Or both. Or none. You'll figure it out.

You need separate relays and switches for each horn.

>>932313
Are those the two horns you want to select in your pic? I would suggest using a seperate relay for each one. Connect both terminal 30s to the fuse. Connect each horn as shown in your pic. But install a SPDT toggle switch between your horn switch and each relay's terminal 86. That way, the selector switch will only have to carry the low relay coil current.

>>932733
this is how i did my train horns on the truck