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Just use the wire that was for the horn to trigger (turn on) the relay.

 

Ah ok. Horn plug meaning the plugs that connect directly to the horn right? As for the ground on the relay, that should be 8 gauge as well correct? Also, just to verify, I change the fuse for the horn as well as the horn relay to say 30A if I go with the 5 horns in addition to a 30A relay that will handle all the wires and splitting and whatnot.

 

Each horn can have its own ground which can be the oem wire size. The 8ga is because one large power wire is feeding all the horns.

You don't change the oem wiring or fuse. You need to run a new power wire from the battery with a new fuse and fuse holder to the relay.

 

8 gauge is overkill. At most I would use 14 gauge, MAYBE 12 if I used my horn a lot.

 

Gotcha. I'll head over to Pep Boys and Kragen to see if they have the relay. I have a fuse holder, but it's kinda humongous, about 5" wide and long. I'll see if they have something more compact. Reason why I asked about the ground being the same size as the power is because car audio wise, when it comes to an amplifier's installation, both the power and ground wire need to be the same, otherwise the amp will not get the current it needs.

 

Here's a wiring diagram that shows the horn circuit. The parts in question are highlighted in red.

As Texasscout and ttrank have said, you don't need to modify the OEM wiring. You'll just need to tap into the horn trigger wire which, in the diagram, attaches to pin 1 on the horn relay.

Also, since each horn will be grounded separately, and each horn only draws a max of 5 amps, the ground for each one only needs to handle that much current draw. That's why they don't all need 8 gauge ground wires.



Edit: I should probably mention that I stole the wiring diagram from the Factory Service Manual so graciously hosted by EricIsKlumzyee. There is a link to it in this thread:

https://g35driver.com/forums/faq-diy...df-format.html

 

I just ran a #8 wire, fused for 30 amps, from the battery to the horn area. I came off the Green Red (G/R) wire in the horn plug using a spade terminal and went to the coil of the relay. From there to ground. then the hot from the battery to the points and from the points thru the air pump of the horns to ground. You don't need to change the fuse to anything bigger. In fact I ran the thing direct using the factory wiring for a while but the voltage drop was just too much and the horns were not that loud. With the extra relay, it will get some real attention.

 

Been a while since I've done anything, but I got everything wired up and still, doesn't sound like it should. I used the relay as well. It seems that I need to get the wire directly from the horn to the really I installed.

Anyone know where that wire is and how I can access it?

 

Bump, need to know the direct source of the horn wire from inside since that 15A relay is still causing me issues.

 

If you are using the horn wire only to trigger the relay it should not cause any issues. A standard automotive relay only needs 100mA to trigger. That line will provide 150X that.

 

Maybe my issue is the horn trigger wire and I am thinking I have the correct one hooked up. Is the horn trigger wire the one that is the positive wire that connects to the OEM horn? If not, where is the horn trigger wire?

I think that's the problem, because the horns are not loud as they should be. That original fuse is still limiting the power these horns should see.