Crazy horn question

[Ford.P51]

Our 72 Challenger just failed an inspection, the horn didn't work. Funny thing is the horn works with the key off, but doesn't work with the key on. 

Any ideas/suggestions? Bad relay? Bad wiring to the relay?

[Chryco Psycho]

has to be something to do with power not being there with the key on , start checking at the realy on the fuse box , no cicuit I can think of is on & shuts off woth the key on though

[Ford.P51]

Yeah, I've never heard of a circuit that loses power when the key is on.

I'm going to pickup the car here in a few minutes and take a look. Definately something strange with this one....

[Ford.P51]

Well, I haven't solved this one yet. On the drive home the horn worked while driving. 

When I got home, turned the key off and the horn still works. Then I restarted it, no horn. A couple minutes of idling - and the horn worked.

I'm thinking maybe the relay isn't working correctly, maybe voltage is low at startup.

[Bullitt-]

I'd speculate a poor ground either at the horn or horn button.

[Chryco Psycho]

Relay could be bad as well

[MEK-Dangerfield]

Take the center cap off your steering wheel and look at your horn switch. That needs to be firmly grounded with a good clean connection. Also make sure that black wire connecting to it, is firmly in place.


  Mike

[Ford.P51]

An update: apparently ground is lost on the column when the key is switched on.

Using an ohmmeter I could see that I had a good ground on the column with the key off. Press the horn switch and ground to the black wire is good, horn comes on. Turn the key on and the ground on the column disappeared.

So .... where is the source of ground to the column suppossed to be? I'm guessing either thats bad or there is a serious wiring snafu in/around the ignition switch.

I ordered a service manual, it hasn't arrived yet. The previous owner was a real butcher when it came to fixing this car, nothing he touched was fixed correctly, usually as cheaply and as crudely as possible. I see evidence that he cut and spliced wires around the fuse box - I'm worried about how badly he hacked up the wires down there.

[Bullitt-]

Bizarre....here's something to study in the meantime.

http://www.mymopar.com/downloads/1972/72ChallengerB.JPG


http://www.mymopar.com/downloads/1972/72ChallengerA.JPG

[Ford.P51]

Thanks for those bullitt99 - I think I grabbed those from one of your previous posts (a successful search!). 

[Moparal]

Not sure if this helps

When Chryco came down to see me. I had noticed that my radio came on when I put the key in the ignition even without turning the key. Just recently I fixed that problem. The radio was a factory am/fm out of a 70 fury with mutiplex stereo. Mine was a factory am with front rear fader.

When I hooked the power lead up from the fm radio, I hooked it into the wrong plug in on the harness. It took a bit to figure that out maybe an hr or two. You may just have something plugged into the wrong place. When the key is installed the key buzzer should go off with the door open. This has wires that go to different areas in the harnes. Rigged wiring hooked up to certain areas with cause ill effects on diagnostics. 

I would assume you have a plug in , in the wrong place.

[Chryco Psycho]

I found this exact same thing in another car , there is another similar plug in the same area

[Aussie Challenger]

  I found a few years back a car ( non MOPAR ), that the steering shaft itself wasn't grounded, there was a ground wire bridging across the flexable coupling that was broken, I cannot check mine until the weekend but did MOPARS have this wire?   

[Moparal]

Some other types did. The dash is grounded to the body frame. The gauges are grounded to the dash frame. The column is grounded to the dash frame. All is grounded to the battery by the wire harness in areas all over the car. Keeping the grounds clean and tight makes for good operations of electronics.  If you have a harness area not getting good contact. It affects the area that the harness suplies.

[Aussie Challenger]

  The horn grounds down through the centre steering shaft which sometimes doesn't make good contact with the outer steering column, especially if the shaft has plastic bushes instead of bearings.