My horn in my 72 f100 isn't working... I do not have a horn connected at the moment but I was testing for power at the wheel. At first, the tester indicated power at the wheel and when I tested, I could hear the relay clicking as I grounded it. For some reason, it stopped showing power there and has not since. I am getting power to the relay and I have replaced the relay and still have not gotten anything. All my fuses are good as well. Is there any other reason why I'm not getting power at the steering wheel?

 

These kinds of questions are a little tricky to answer because the people who know how to fix electrical also know how to trouble shoot and it isn't just a throw another part at it solution. It's basically pretty simple, get a good test light and start tracing the power (and grounds)

 

There is no horn power at the wheel.
The horn button grounds the relay.
Check the wires on the relay,
1 will be B+ , 1 will go to the horn, 1 will be ground when horn is pressed.

When the horn is pressed, the relay gets a ground, closes, and sends B+ to the horn.

 

dang. I hate tracing wires haha. It makes it harder since all the wires in that area are wrapped together and then go into the firewall on the passenger side and are wrapped all the way over to under the dash on the drivers side where there is a whole mess of wires... And shouldn't there be power at the wheel? Or else there is nothing to ground? One terminal on the horn button hooks to the power, the other to a ground, then when you press it, it grounds the power thus grounding the relay and sounding the horn right? I really hope it's not a connection problem in the steering column bc I don't want to pull the steering wheel...

 

A yellow wire fusible link at the starter solenoid is what sends power to the horn relay. Power goes from there up the steering column to be grounded by the steering wheel horn switch. I believe this is a yellow/green wire. Check for power now at the horn relay. If none there replace the fusible link. If there is power there at the relay goining in it and back out then check the yellow/green wire top and bottom of the steering column.

 

FYI.. the OEM rag joint has a copper bridge to ground the horn button. Mine had broken so a short wire with eyelets connecting both sides of the rag joint jumps the electrical gap.

HONK!

 

No
No

You do not "ground a power wire" (that's called a short)

The horn relay is a switch, it has constant B+ on one terminal.
The second terminal goes to the horn. (this will be 12v when the relay is grounded)
The third terminal goes to the horn button. This is not a power wire, it is nothing until the button is pressed, then it is a ground circuit.

You need power and ground for the horn to work.
The relay is fed a constant 12v, when the relay is grounded (via the horn button) it closes and allows the constant 12v supply to go to the horn.

 

well idk how it happened but I was getting power at the wheel for a very short time... maybe had something grounded by accident? So just to clear this up, when I touch my test light to the terminal at the wheel, I should not get any current, correct? Or should I since the test light is essentially just a ground?

 

12ozd I hate to start a war here but your not quite right. The wire going up the steering columb will have 12 volts on it until it is grounded. If you look at the wiring diagram that is the ground side of the pull in coil in the horn relay. So as long as it is an open circuit it will show power. Push the button down closing the circuit to ground and then you will not see power on that wire. You do not have excess current flow either because the coil is a controlled resistance. But you do now have an electromagnet which will pull the contacts closed in the relay which will blow the horn. The OP said there was power there originally so either there is a poor connection, broken wire, a bad ground at the horn switch,or possibly a bad new horn relay. Three wires at the relay. With connector unplugged from relay one terminal should show battery voltage. Plugged in if pull in coil is good you should then find power as a second terminal. That would be the one going to horn button. If you ground that terminal then horn should blow, which is the same as pushing down on the button. If it does than the problem is between relay and ground at the horn button. If not and there was power at relay than either a bad relay or horn. Horn can be tested by seeing if there is voltage to it when relay is energized. One poster mentioned a ground wire at the rag joint. That is a good point you do need a good ground on the ground side of the horn switch.

Hope that does not start any wars as 12ozd is correct in that it is the ground circuit for the relay but you will see battery voltage on it until it is a closed circuit.

 

Depending on your test light, the horn may even blow.
(your light would be providing a ground for the relay)
Not the first time I've heard that.

Maybe I was trying to oversimplify the explanation, maybe it was just a bad explanation.
The point I was trying to make was; the relay gets grounded by the horn button, it is not not a power supply.
I was reading that the OP was looking for a power and ground source for (at) the button.

Technically ihc1470 is correct.
I was trying to give a more simple explanation of the circuit.
A "horn 101" response, instead of a "electrical 102" one .
(not a sarcastic answer)

Same here, if I contradicted any other posters, it was in the attempt to (possibly poorly) explain, a fairly simple circuit w/ out being to technical.

JEFFFAFA would be correct in that the wire from the relay to the horn would show power, that would actually confirm the power to the relay, the wire and connections from the relay to the horn button.
Hope my attempt to help didn't further confuse the question.

 

[QUOTE=ihc1470;14877169]Push the button down closing the circuit to ground and then you will not see power on that wire.


So since a test light is connected to a ground, should it not light up when touched to the terminal on the steering wheel?

 

Yes you should see power however a better place to test it would be where it goes into the column. At that point you should see power and your eliminating the slip brushes and ring at the steering wheel. If you do and not at the top end then pull the steering wheel and see what shape the brushes are in that push against the steering wheel. Or you might try tapping the wheel and turning it while holding the test light to the terminal. It is not unusal for the slip ring to be bad or brushes wore out. Be sure to put a little grease on them when you put the wheel back on.

 

okay, thanks. Is that the yellow and green wire? Or maybe it's yellow and blue. I don't remember

 

That I can not tell you. Look at the relay, normally it would be the same color wire all the way through.

 

OP's truck is a 1972, does not have a horn button (or a horn ring).

1971/72 F100/350's have a 2 spoke steering wheel, use a vinyl horn pad that contains the horn switch.

The horn works thru the T/S switch...below the steering wheel is the horn brush (13A824 in pic).

The horn brush contains a thin copper wire that snaps, horn no longer blows as a result.