Review on 🚂 150DB Air Train Horn Kit for Car, Loud Twin Tone Chrome Plated Zinc Dual Trumpet with Compressor – Ideal for 12V Trucks, Lorries, Trains, Vans, Boats (Silver) by Dee Parson

In the instructions you run the blue and yellow wires from the relay to the horn button (if you choose that option) but you need to run the blue wire to the horn button and the other side of the button needs to be grounded and the yellow wire must be connected to relay red/hot wire. Here's how I did it and it worked. Horn sounds very good. It's not a train whistle, but it will still scare people. he he he