Horn works, except if Lights are on???

[Diastole]

Good mourning? Before I tear into the switch, steering column, etc., I thought I would pose the question to all you experts and see if ya'll could offer a noob to Model As (but, full of late 50's GM knowledge and experience, amongst other useless things) any advice?

All thoughts are helpful. My guess is contact plate problems.

1) The horn works and sounds well when lights are off. This is a new problem. Worked well three months ago, just finished replacing headgasket, manifold gasket, muffler, rebuilt water pump, checked rear mains, replaced oil drain tube, changed timing gear, and had to rotate steering column to align upper plate arm to distributor housing.
2) whether the engine running or off is same phenomenon with horn
3) car is stock, 6V positive ground. 1930 early Standard Coupe, oval speedo.
4) the voltage at the horn is 6.39 volts and at the battery it is 6.47 volts.
5) incandescent 2 bulb headlights. No cowl lights.
6) the lights do not dim and the ammeter does not deflect more when the horn button is depressed and the lights are on. Suggesting NO Connection
7) new condensor. The modern one, new from parts supplier failed after 3 mos. Measurment showed .36 nanofarads not the 242 nanofarads needed

Thanks in advance, us newbees always appreciate your help and assistance.

Diastole in the Smokies

 

[katy]

re: 6) The headlights and the horn are not wired through the ammeter, they are powered from the output side of the generator cutout.

The horn button supplies a ground going through the centre of the light switch, I would suspect that is where your problem is.

 

[J Franklin]

You can add a horn relay to pep things up.

 

[The Master Cylinder]

You can add a horn relay to pep things up.

That's what I have been planning to do. My horn works great with the engine revved up, not so good at idle or parade speed. Shouldn't be hard to do.

 

[Rob Doe]

Bring battery to full charge.

Remove the horn cover. Lube the horn's armature at both ends with a drop or two of light oil on the felts.

With the engine off, turn the lights on.

Take a voltage reading at the horn where the yellow wire connects to the horn. Take this reading while the horn button is fully depressed to blow the horn. (current flowing)

A low voltage reading, less significantly less than battery voltage, means dirty / loose connections / bad wires between the horn and the battery. Clean ALL power side connections from the negative battery post to the horn. Clean bright and tight.

When the voltage reading is near battery voltage, use a jumper wire from the output side of the horn to the battery positive post (best choice) or known good ground i.e clean head nut, radiator shell, etc with the horn button depressed. (current flowing)

Look for obvious faults with the horn's wire connectiors, the windings or filthy armature commutator and brushes, etc. If still no horn, your horn may need windings and a rebuild.

Perform the voltage drop tests described in Chapter II of the Les Andrews blue book "Troubleshooting and Diagnostics", specifically the tests of the headlights.

Katy post#2. I'm having trouble with your comment "The headlights and the horn are not wired through the ammeter, they are powered from the output side of the generator cutout."

The horn on our coupe works fine without the engine running / alternator / generator turning. So, what is supplying the current for the horn? The battery, right?

 

[katy]

Katy post#2. I'm having trouble with your comment "The headlights and the horn are not wired through the ammeter, they are powered from the output side of the generator cutout."

I stand corrected, the power does go through the ammeter before it gets to the output side of the cutout.

 

[rotorwrench]

The horn takes a high rush input of current and the lights just use a lot of current to function. The generator output may be low if it still has a three brush generator. A person can measure the load that the horn draws to see if it's drawing more than it should. Just place an ammeter in the power line to the horn.