Horn Diagnosis

[67RT]

Hi,

I am troubleshooting a dead horn (never worked). All other electricals work on car except dash lights, and that may just be a bulb. Turn signals and hazards function properly.
I bought a good horn and verified a honk when I hook it up to battery power and ground. I have no power at blue/yellow wire at horn when pressing horn button. I am chasing it back thru the column. From what I have read, contacting the two copper contacts on springs should close circuit and give me 12v at the horn. It doesn't although it does read 12v on the meter. When I jumped the hot copper contact to the center nut on column I got sparks and briefly some smoking wires from within. I am thinking that the hot wire is open in the column and shorting here. Any thoughts?
So to fix it I need a new turn signal switch, which also includes the horn contacts?
Mine is a 1970 so there is no relay. Everyone seems to think I should install one. Is that the case? If so, I will try to follow the thread below. Seems tricky..
http://classicbroncos.com/forums/showthread.php?t=249877&highlight=horn+relay

 

[JAFO]

Right, 70 would have no relay. Mine is a 73 and also no relay. Yes, shorting those two posts should make 12 volts at the horn. And so one side of the horn is fed the 12 volts from the column and the other side of the horn is grounded. Those two contacts at the column, that the horn button shorts, they do not contact ground. Those contacts are basically a switch you are closing when you press the horn button, sending 12 volts to the horn. So one of the contacts should read 12 volts and the other nothing. The one reading nothing should be going to the horn.

I did install a relay on mine. So, still 12 volts goes through the column and instead of feeding the 12 volts to a horn, it feeds 12 volts to a relay and I ground the other side of the relay. And then I fed 12 volts to the relay contact and the other side of the contact feeds my horn.

Later models ground at the horn button at the column instead of the horn button being a path for the 12 volts. Main thing about having the relay is that lower current is flowing through the horn button contacts.

 

[67RT]

Thanks. So can I replace my stock turn signal switch with the proper 1966-1973 two prong switch and still wire up with the relay as shown above so I can keep the same stock horn button?

 

[JAFO]

I have some thread where I was wiring up the steering column connector in my Centech harness and I noted the various connections. I did install the proper turn signal switch into my 1973 and did wire in a horn relay, but the relay is out in the engine compartment and I used the horn wire from the steering column that ran to the horn to power my relay. Know what I mean? I will find that thread regarding the wiring.

 

[JAFO]

Here is that thread regarding horn and column wiring...

http://classicbroncos.com/forums/showthread.php?t=260944&highlight=column+wiring

 

[Steve83]

There are SEVERAL "correct" ways to add a horn relay. The way Ford did it was to run UNswitched (B+) power to a special relay (3 terminals) under the dash, but you can use any common relay (4-5 terminals). B+ goes to both the power input and the relay's trigger coil. The other side of the trigger goes to the horn switch on the column, which grounds that circuit when you press the button. The power OUTput from the relay goes to the horn, which is grounded at the core support.



But it would be easier, quicker, & cheaper to just fix the fault in your original wiring. If you don't, you'll have to pull at least 2 new wires to add the relay, and those same 2 wires could be used to overlay the originals, making the original circuit work.

 

[67RT]

The turn signal switch still works, but there were some little broken plastic pieces under the horn button, so I may need the whole switch. I bet it has worn thru and it touching the steering wheel bolt. I really appreciate the tips and I know how to use multimeters and wire a house, but little experience on cars.. What is the worst that can happen?

I was looking for a FLAME icon...

 

[JAFO]

On the 73 and earlier that piece on the horn button is insulated so that it doesn't touch anything grounded, so yeah there are some plastic insulators under it. I wanted to keep all my wiring intact, so did my relay version out in the engine bay. Everyone solves problems differently. As long as it works and like you said, nothing melts, you should be fine.

I had installed a new steering wheel as well as new turn signal switch. I wired everything up and horn wasn't working. I found the fuse blown. Replaced and pushed the horn and the fuse was blown. Had me scratching my head for a bit. Ended up finding that the brand new aftermarket steering wheel had a bent tab (that one that touches one of the horn contacts) that was touching the other metal on the steering wheel and shorting it to ground. I had to bend that tab away so it was isolated, then all was good. Always something.

 

[67RT]

Ok, I have a stock wheel but did read a thread where that may be an issue. I will pop it again this weekend unless it gets cold and report back. Not many 75° December days in the DC Metro. I LOVE it..