Problems With Car Horn!!!

Hi, I have a mercedes 190e and a Prestige APS785 and I install the Horn Output to my car horn, I use the relay this way 87: 12V Fused 86: 12V Fused 85: Negative Input 30: 12 V Output To device It works the first time, When I came back and I Unlock the alarm it did not work anymore. What could be the problem?

Well, all you have to do is test all four connections at the relay to see if they are still doing what they're supposed to do. But I just thought of something. Don't most European cars disable the horn when the key is turned off? Try remote-starting the car, and then arm and disarm the alarm...does the horn work now? If so, there's your problem. If that's it, you'll just have to wire into the horns somewhere AFTER the keyswitch, so it'll work anytime. I'm not at all familar with how Mercedes wiring is. If you have access to a service manual, you might be able to find a spot where you can connect your wire inside the car.....but if you don't have that information, it would probably be simplest to run a wire under the hood and go directly to the horns.

what I did is that i have connect the wire under the hood dicrectly to the horns. About that when the Key is urned ogg the horn doesnt work i will try with the remote star. thank you