I’ve got myself a set of Cadillac 4 notes I’m planning on installing, but I’ve heard you need a 2nd relay. my plan is to pull the fuse box and splice into the wire for the horn button so that it’s the ground signal for both relays. What I’m trying to know is if this sounds correct or am I missing something. I also don’t know if I can get to the wires enough to splice

 

Use a relay near the horns that has battery voltage to it and triggered by the existing horn wire.

 

that’s the goal. What I don’t know if the wires under the fuse box are too packed to splice into.

 

why do you have to go under the fusebox?
There's always the positive battery terminal.

 

I need to splice into the signal wire from the horn to activate the 2nd relay. The supply wire I’m going to hook to the battery

 

are you saying to have a 12v signal via the existing horn 12v?

 

Use the original horn wire to excite the relay, giving battery voltage to the new horns.

 

No, get ground from the original horn connector and give it to the 2nd relay. Take 12v from the battery terminal, PDC terminal, or fuse tap.

 

Here's how I've been doing it for 55 years: