Dual Horn Installation Question

[smitkea]

Hey guys,

I plan to install an electric air horn, while keeping my stock horn, that I can sound by turning on a switch and honking the stock steering wheel switch.

This is my plan so far:
85: - ground
86: + wire from switch
30: + from stock horn circuit wire (battery end of cut stock wire)
87: + out to air horn
87A: + out to stock horn (horn end of cut stock wire)

Seeing as I have never worked with relays or amps (besides basic sub installs and some LEDs) I have a couple questions about doing this, in order of importance (in case its too long for y'all to read )

1. Do I need to worry about overloading the wire in terminal 30? I know my air horn is an 8 amp input, but I don't know what the stock horn circuit is capable of handling.

2. When cutting the stock horn wire, where should I make the cut? I know it goes from the switch through a multiplex, through a horn relay, then to the horns, so should I just snip it close to the steering wheel before it goes to those other components?

3. Do I need to worry about the amps of the driver's side fuse I choose to splice? The switch I am using is rated for 20a.

4. I plan on using 12 gauge wire all around, this should be plenty thick enough I hope?

Sorry for so many questions, and thanks in advance for helping this newbie!

 

[smitkea]

Please help! Any help is greatly appreciated!!

 

[xci.ed6]

So you want the horn to work key off?

Draw a diagram.

 

[smitkea]

Sorry if its confusing. Yes I want either horn to work when the key is off/acc/on. Like my forum skills, my diagram skills arent the best but here is my plan drawn out in paint:

imgur (dot) com/fZZYe6S

I havent been a member for 7 days so I cant post pics/links. I put pink dots on the stock horn circuit wire to illustrate what I mean by cutting it and splicing the relay into it.

Hope this helps! TIA

 

[smitkea]

imgur (dot) com/fZZYe6S

I put pink dots on the stock horn circuit wire to illustrate what I mean by cutting it and splicing the relay into it.

I just learned the horn wire is a ground wire, so the terminals 87, 87a, and 30 should be grounds in my diagram. (At least I'm pretty sure.)

Edit: or worse... Does that mean I have to splice the positive after the relay in the engine bay, then run it back through the firewall to the air horn module?