Here's what I did on my truck based wooidie and my tonner panel, soon to do on my 47 tonner pickup. Period Ford starter relay as a horn relay. The center (small) post is activated when grounded. I mounted the relay on the back of the horns, ran the small ground wire up the windshield pillar and out through a hole in the header. Ground it to some bare metal and HONK. I made a simple wooden rocker switch that connected with ground on the windshield header, although a store-bought spring toggle switch would work and ran a nylon cord attached to a point over the rear window. Reach up with your right arm, yank the loop of the cord down, HONK! In last years july 4th parade I couldn't keep my grand kids away from it. Both trucks have very loud dual horns. Something about the overhead yank of the trucker's horns. I highly recommend it for a truck.