Yet another horn problem.

[Gonemad]

I recently bought a genuine Lucas horn from my regular parts supplier, Roger, and having read and noted the lable that had the word 'Works' on it I got the bezel rechromed and painted the case with a shiny new plastic paint. It looked terrific so I put it on the bike.
However, when I pressed the button all I got were some feeble clicks from the horn. So today I took it back to the supplier as I needed a few other bits anyway.
The horn did not work when Roger put it on his bench but with a little screw of the adjuster screw it beeped happily away when connected directly to a 6V battery.  "Good", I thought as I drove home.  When I put the horn on the bike... it was exactly as it was when I first heard it. The only way that I can get it to toot is to connect it directly to my own battery, as Roger had done on his bench with his own battery.  With any intermediate wire, it's just 'click'.  I tested the circuit from the button to the supply wire ends, complete. The old horn on the supply wire ends, it works.  The new horn directly to the supply wire ends... nuffink.
Was the wire from the horn to the supply wire ends too thick (desperation setting in now)?  I tried with a thinner pair of wires, nuffink.
I cannot understand it. The only way that it works is with the horn directly to the battery.
I simply cannot understand why it will not work when there is a bit of wire between the battery and the horn but it will work when coupled directly to the battery. Can it be that a metre of wire has just enough resistance to lower the supply of electricity to the horn?

I did read the previous thread regarding the horn that would not work and soon I can get a chum with a dial indicator to go through the checks as detailed by Trev.  Maybe that will sort things out.

I have also thought about the idea suggested by Cyclobutch and using the old horn that used to live under the seat for the MOT.  That horn works perfectly well.  But the thought of having a dead £120 ornament horn just for the cosmetics is just a bit too much for me.

Any thoughts anybody?

Angus

[trevinoz]

Angus,
           I would say that it is one of two things.
1. You have a poor connection between the horn and earth. Be it the push button or the path through the bars and head bearings.
2. The horn adjustment. The points shoud be adjusted so that the current draw is no more than 4 amps, from memory.
Your wires cannot be "too thick", rather "too thin" can be a problem, causing excessive voltage drop.
Which Altette do you have? There are 3 or 4 different ones used on the A7/10 and more if you count the pre-war types.

 Trev.

[wilko]

There will always be a certain voltage drop through the tortuous path from button to horn. Use as thick as possible wire right up to the button as you can. Then holding the button down with your 3 hands slightly adjust it either way while it's mounted until you get a decent sound.

[muskrat]

 Also try running a earth wire from the headlight shell (or anywhere else up front) to the battery.
Cheers

[iansoady]

The button just earths the return side of the horn through the handlebars, steering head bearings, grease, paint etc (horns always have the earth side rather than the live side switched). Plenty of opportunity for a poor conduction path there - just clean everything and as Muskrat says a separate earth wire is always a good thing.

[Gonemad]

There are days when this highly successful structural engineer has to remind himself that electricity is a black art, and this has been one of them.
Looking again at the problem and noting Ian?s comment I decided to start with Muskrat?s idea first, a seperate earth wire, as it was the easiest.
Initialy I put the horn on the bike and pressed the button: Nothing, as before.  So I took a wire from the horn to the handlebars and pressed the button.  Bingo, it worked.
Now, here comes the black art thing. With the wire removed I pressed the button again.... and the horn worked again.  It has continued to work ever since.  It?s black magic.
Not a great sound actually but not that bad either, so I will do as Wilco suggests and adjust it now that it works so well, and as Wilco says again, I will connect  a proper earth wire somehow.
Ian echos a thought that I had this morning. Between the handlbars and the frame are the steering head bearings which, following the principle of lubrication, float on a film of grease.  How on earth can you get a reasonable electrical connection through that?
Trev, Wilco, Muskrat and Ian, thanks very much again lads. Your help is so very much appreciated.
Have a good Christmas boys.
Angus.

[wilko]

You must be using Lucas grease!

[Topdad]

Angus ,you would wonder how on earth  (sorry ) you could pass a circuit through grease etc but I can recall fx4 taxis having there rear wheel bearings go due to earth straps not being replaced between engine and chassis at the required point (lazy mechanics ) and the only earth that could be found for the starter was via the bearings ,they git very hot grease melted beraings ran and brake linnings covered. Electrics as you say a black art!!. best wishes BobH.

[RichardL]

I am prepared to speculate that the designed ground path is via the throttle,  brake and clutch cables. Given these three paths, there is enough redundancy to assure the safety issues of a working horn and an engine that can be killed.

Richard L.

[iansoady]

Angus ,you would wonder how on earth  (sorry ) you could pass a circuit through grease etc but I can recall fx4 taxis having there rear wheel bearings go due to earth straps not being replaced between engine and chassis at the required point (lazy mechanics ) and the only earth that could be found for the starter was via the bearings ,they git very hot grease melted beraings ran and brake linnings covered. Electrics as you say a black art!!. best wishes BobH.

I am prepared to speculate that the designed ground path is via the throttle,  brake and clutch cables. Given these three paths, there is enough redundancy to assure the safety issues of a working horn and an engine that can be killed.

Slightly O/T but I once had a Minivan. I wondered why it was sluggish to turn over till it eventually started and raced at around 6000 rpm. The earthe cable to the engine block had snapped, the starter was earthing through the throttle cable and had melted the outer, welding it to the inner.......

[Gonemad]

Manosound and Ian:  Hundreds of years ago I had a Lotus Elan that snapped a couple of heated throttle cables before it dawned that one of the many the earth wires was broken and the car was earthing through the throttle cable.

Again, Manosound ,  I really would not be surprised if you are right about the designed ground path.  What  surprises me is that so many nutty ideas within the British automotive industry ever gained credence considering the huge number of people involved from shop floor to engineers to management. Surely somebody would have said.... ?Errr, wait a minute....?

[RichardL]

?Errr, wait a minute...."

, how about a little ground strap here between the headstock and the upper yoke? Naaah.

[BearKat]

There is one man that comes to mind when these problems arise and that is TAFF THE HORN  01792 233792,you can find him on internet.He has been rebuilding altette horns for many years and as far as i,m concerned ,THE BEST.