Why doesn't my horn work?
 

My horn stopped working, and I can't figure out why. I can hear the relay click when I hit the horn button, and my voltmeter says 12 volts at the horn wires when I hit the button.

Based on that I thought the horn was bad, so I bought a new pair of aftermarket Hellas. I got a short blip out of one of them, then nothing. Neither horn works at either connection. I tested them directly across the battery and they worked, even the old one I thought was broke.

When neither horn is connected, I still get 12V at each connection and I can't find any blown fuses. I also can't find a fuse that's labeled horn, either though. What am I missing?:confused:

Perhaps your problem is at the steering wheel/horn button. Is the horn wire connected? Is the contact "contacting'? Any corrosion? Good luck. Also, IIRC there is a horn relay on the main fuse panel, not a fuse.

The horn button works fine, and the relay appears to work fine too. I did pull the relay and clean off the contacts. When I hit the horn button on the wheel, I hear the relay click, and when the horns aren't connected, I get 12V at the horn wires.

It sounds like an intermittent ground problem. If the '73 is like my '86, the brown wires at the horn connection should be grounded nearby. The local grounding point may be corroded or have failed. When you tested for voltage at the wire connectors, did you touch the negative lead to the ground connector or to the car's chassis? Did you test for voltage with the horns mounted and connected?

If you get voltage at the connectors, then there can't be a blown fuse so no need to look for one. If there were an electrical short in the circuit, the fuse would certainly blow. I'll bet it's a loose connection somewhere at or near the horns.

Sounds like corrosion some where.

Check the relay socket for corrosion. You will need to get clever to clean out any gunk.

You can check for a bad ground by removing the brown wire from your horn and use a good wire to connect the post onthe horn to the negative battery post. Hit your button, if you horn works ok then, it is a bad ground.

When I tested for voltage, I had the driver side horn mounted, with the body ground mounted to the same bolt. The horn wires were not connected, and I connected my voltmeter direct to the horn wires.

Try testing for voltage when the horn is connected and mounted. You've already determined that the horns work, so if there is voltage they should sound when you press the horn button.

However...you also need current. Corrosion, worn contacts or a loose connection anywhere in the path between battery positive and the horn can add resistance. Enough resistance, and there won't be enough current to drive the horns. You verified the horns work by connecting them directly to the battery posts, so there would be no resistance in that connection.

Harry gave good advice too. Make sure all your fuses are making good contact in their holders.

Thanks for the suggestions so far.

I cleaned off the ground contact and still no luck. Doesn't make any sense to me. I know that without the horns there's power there. With the horn connected, the voltage across the horn is much less than 12V. What the heck am I missing?

I had to take apart my horns to find the contacts underneath rusted, cleaned up an insured it worked by putting a 12volt source to it.

%#$& electrical problems. I cleaned out the relay socket real well, and sure enough, both horns work now. Thanks everyone for the help.