I need help wiring up a new 12v horn. Its a dual horn. Each one has two wires coming from it but are both grey which I assume are ground and power. I tested the new horn by hooking up to the battery directly so I know it works. Anyway my problem is I can't get it to work with my steering wheel horn button. I tried wiring it a million different ways after reading a bunch of threads and having my own ideas but nothing seems to work. What ive gathered is that theres two wires for the stock horns. A yellow/blue wire which is power and a dark blue which goes to the factory horns. The trucks a 1986 f250 without cruise control. If someone could tell me what wires to hook up to a relay or togethor without a relay that would be greatly appreciated.

 

Does the stock horn(and wiring) still work?

 

Before I unhooked it only the driver side horn worked. The passenger side didnt work. When I was trying to hook up the new horn I was using the driver side dark blue wire from the factory horn.

 

Hook the two factory wires up to your two gray wires first one way, then the other?

 

Only the dark blue is visible in the engine bay. I found the yellow/light blue wire on the steering column but couldnt find it in the engine bay.

 

The factory horns only have the one dark blue wire going to them but the new horns have two wire connections.

 

Ground one terminal on the new horn and hook the other to the wire from the switch.

 

I tried that because it makes sense but it didnt work. I read this morning that the dark blue wire turns into a ground wire when the horn button is pressed and the factory horns are always hot. That thread was in the superduty section but I think it might still be the same system. Would it then make sense to hook the dark blue wire to the new horns ground wire and then pull power from the battery with the other new horn wire?

 

IIRC, on a truck of your generation with no cruise, that doesn't apply. The circuit goes battery -> fuse -> wheel button -> horn -> ground (factory horn is grounded by its mounting). No relay. Thing is, this aftermarket horn may draw more current than you'd want to put through the column wiring and wheel button(s). You may have blown the fuse, actually. The way I'd do this is:
* Check/replace fuse, and check voltage at the wire that drove the OEM horn. Should have 12V ONLY when someone is pressing the wheel pad
* Connect that wire to the coil circuit (terminal 85) of a standard automotive relay
* Connect the other side of the coil circuit (terminal 86) of the relay to ground
* Connect a wire from the junction point on the starter relay to a stand-alone fuse, and then to the "power" side of the contact circuit (terminal 30) of the relay
* Connect one of the leads of the new horn (whichever one the mfr considers "positive" to the "load" side of the contact circuit (terminal 87) of the relay
* Connect the other horn lead to ground

With this configuration, the horn button will energize the coil of the relay, which will close the contact circuit, which will power the horn itself from the stand-alone fused circuit.

 

This is really helpful. I'll give it a shot after work. Thanks a lot!

 

I have been so busy with work that I didnt get a chance to look into this until today. Blown fuses like you said and after replacing them and following your directions it work flawlessly. Thanks again!