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MG TD TF 1500 - Horn Push question

I am trying to sort out a problem with a friend's '51 TD.

The push button for the horn was "self-activating" intermittently, and would not always work when pushed.

I originally diagnosed it as a badly worn spring beneath the push-button, and since the spring in the headlight dip switch was also weak, my friend decided to replace the assembly with a new one from Moss.

I have discovered that when the button is pushed on the new assembly, a "dead short" is set-up and the spring overheats, and loses it's "springiness"(new word?)

When pushed there is a 15 amp draw on the ammeter.

I then tried a used "toggle switch" from an old MGB, in place of the new horn push button, and the horn works fine. There is still the substantial draw, but no sparking, or overheating is present.

I am lothe to condem the new Horn assembly, but can't come up with another suggestion.

Any input would be most welcome.
JR Ross

JR the horn/dip switch I got from Moss was not wired correctly. It caused a direct short. I had to take it apart and rewire it. I made them aware of it also. Thought I might have just had a bad unit but apparently not. Look it over and I'm guessing you will find all of the wires off one terminal in rotation. I don't remember which direction. It got hot enough to melt a bullet plug off before I cut the power. If you find yours is the same make sure you let Moss know about it.
LED DOWNEY

If you find the same thing I did then you must emphasize to Moss most strongly that they check all their stock before somebody burns a TD to the ground.


LED DOWNEY

jr, when you say the last switch did not work, but yet the horn would 'self activate"..makes me think you may have a different problem here..perhaps.
what do you think of this idea?..the horn switch supplies the ground to complete the circuit and activate the horn. if the last switch did not activate the horn..it was out of the circuit. the circuit was getting ground somewhere else..i.e. a short to ground. 15 amp draw seems like a big number. my amp meter only goes to +/- 20 amps and i only see about 2 amps on the gauge when i push the horn switch. regards, tom
tom peterson

JR if you look at the picture I posted you will see that all of the wire leads need to be moved one pole in a clockwise direction. This is as it was sent to me. The blue lead is the power lead for the lights but as you can see it is fixed to the horn circuit. Push the horn button in this position and you have a direct short to ground along with the voltage from the horn circuit and you get the double whammie. Since the lighting circuit is not fused you can release all your Lucas smoke in a hurry.
LED DOWNEY

what are the boards thoughts about "there is still a significant draw"..comment. i only show about a 2 amp draw. regards, tom
tom peterson

FYI, the horn current does (should) not go through the ammeter. Bud
Bud Krueger (TD10855)

Thanks all for the input. I think that I am looking at a couple of problems.

1. As mentioned the horn works using a "toggle switch, but still has a "significant draw", according to the Ammeter. This says to me that the car's wiring may be incorrect, since the horn apparantly shouldn't register on the Ammeter.

2. All of the colour coding on this car's original dash wiring is "faded" to the point that one wire is unrecognizable from the others.

3. All of this is compounded by the fact that a DPO has "altered the car's wiring in a couple of places (and done a very amateurish job of it), and there have been a few "modern" wires added.(for unknown reasons)

4. The horn push from Moss is wired incorrectly also.

I suspect that I'm going to have to "go through" the entire circuitry of this car and sort it out, before correcting the horn difficulty.
Thanks again for all the input. It sure helps to have more than just my own thoughts.
JR Ross

JR If you can, get copies of the wiring diagrams published in the "Sacred Octagon" as a center fold. These were in colour which made it easier to follow even if the wires were so faded that they could not be identified by there colour. I don't at the moment remember what issues they were in but it was about two years ago now.
Cheers,
Bob
Bob Jeffers

Does anyone know what issue that was?
Richard Taylor TD3983

This thread was discussed between 20/08/2010 and 24/08/2010

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