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MG MGA - A Horn puzzle

I can't work it out, so thought I'd give the crew a challenge

My car has 2 Windtone horns, high and low note. Periodically the horns stop working. In an attempt to resolve this once and for all, I have made up a new harness for the horns, and bought a new high note horn to replace the incorrect old one.

Both horns work perfectly when connected to the battery directly to test them. When mounted under the car, and connected in parallel, the high note horn works perfectly, the low note does nothing.

When I disconnect the high note, the low note will then make a single click when the horn button is pushed, but otherwise does nothing. If I connect to the battery again, it works fine.

All the wiring is in good condition, no high resistances or dodgy joints.

Any ideas?
dominic clancy

Dominic, have you tried to clean and adjust the points in the low-note horn? The horns draw a lot of current, especially if they do not open the contacts.
Chuck Schaefer

Dominic, It could be that you are not getting enough current to operate the horns properly. Assuming that the wiring is of the correct thickness to supply enough current, it has got to be downt to a bad connection, earth or faulty horn button. The horns are fed with battery via their own dedicated fuse (brown and green wire) the live side of the fuse is supplied by a brown lead which should end up on the "A" terminal of the regulator. If this supply is ok you should be able to sound the horns by applying a good earth to the non live (brown and black wire) side of the horns. Watch out, there will be a big spark and if it works, a lot of noise! If that goes ok, the fault is either the horn button or the earth it supplies to the horns. The button earth wire should be black and it is one of those wires that is held by the nurled fixing screws for the instruments on the dash, they could, of course, be loose. If you find no fault in the wiring try adjusting your low note horn with the adjusting screw inside the domed cover.My car has a standard wiring harness and twin windtones, and they work perfectly. Hope this helps. Lindsay
Lindsay Sampford

Dominic

It may be worth trying these horns.

Steve

Steve Gyles

LOL Steve lets hope Dominic does not take the hump!

I tried to google for a icture of someone taking the hump!! and did not find anything appropriate. cough cough!!

Dominic I am sure it is a high resistance story some where but rather than worrying too much about that I would simply adjust the horns in situ and on the horn push.
Robert (Bob) Midget Turbo

Dominic - Lindsay's comments are exactly correct. The horns pull a lot of current and if all the connections are not perfectly done and low resistance, the horns will not work properly. It sounds like you have a high resistance connection in the path to the low one horn (along with, possibly a corroded contact inside the horn). One of the things that you could do to improve the operation of the horns is to add a relay in the circuit, using the relay contacts to provide a ground very close to the horns, with the ground from the horn button supplying the ground to the relay coil to actuate the relay (this is then a low current path that won't cause any voltage drop due to the long wire length from the horn button to the relay. While you are at it, see the article, Electrical Connection Preparation in the Other Tech Articles section of my web site at: http://homepages.donobi.net/sufuelpumps/ which provides tips on how to make secure electrical connections. Cheers - Dave
David DuBois

On a serious note, I am following this thread with interest. I have 5 of these hooters (avoiding the term horns!) on my workbench that I have been trying to tune but without luck. My error seems to be trying to use my 1948 Hornby Dublo model train 12v transformer and controller as the power source - obviously not enough amps.

I guess it's off with the battery cover and tap a bit more power.

On a similar vain, it's probably why the renovation of my old SU pump has stagnated!

Steve

Steve Gyles

Now I dare not google for a picture of some "hooters"
Well not on a British site anyway :-))
Robert (Bob) Midget Turbo

Thanks for the comments

The low horn works correctly when connected to the battery, so it would not appear to need adjustment.

There is enough current at the connector under the radiator duct panel to drive the high note horn, but apparently not enough to drive the low note horn, but not enough to drive the low horn either alone or in tandem. Is there perhaps a threshold issue at play? The wiring harnesses for the horns are new, are of a suitable gauge wire, and have double crimped connections (I have a professional crimp tool) and heat shrink as a strain relief. That one horn works and the other doesn't is the puzzle.

Bob, I didn't realise that Camels had horns....

Steve, I know that even a 12V Car battery charger does not deliver enough grunt to test the horns in some cases (though the low note horn does work with my battery charger, the other one that I have replaced does not.)

After puzzling over this lying on my back on a raft in the middle of the lake this afternoon, I have decided that the next step is to bridge the horn button to see what happens then. Lindsay, your idea is also a good one.

Adjusting horns in situ is a bit of a problem as the domes are on top. Which leads to the question, which way is up?

Incidentally, the new (Moss- supplied) horn had the mounting bracket in the wrong position to be able to mount it, and I had to dismantle the horn and do a considerable amount of fettling to the bracket to be able to fit it in the correct place.
dominic clancy

I would measure the voltage right at the connectors to the horn. When the button is pressed, if it is more than a volt or two lower than the battery voltage then you have a high resistance connection somewhere. Could be the horn button like you said. Another possibility is corroded or poor connection for the lower fuse on the fuse block. Either way, tracing back with a voltmeter will let you find the high resistance connection.
Jeff Schultz

Dominic

My horns were giving me sporadic performance then quit. I ran a points file thru them and all is well. Mine issue was simple. Good luck.
Bill Haglan

Hi Dominic,
Just addressing the problem as a parallel circuit. In theory the horns should have the same resistance so that both will have the same current through them.
Obviously this is not happening - so the low horn must have a much higher resistance than the new high note horn - so a much smaller current will pass into the low note so it doesn't operate, whilst the high does as it takes most of the current. There is probably a fault in the low horn due to corrosion etc.,so it will need dismantling to clean contacts etc. The high current available direct from the battery will overcome the high resistance due to corrosion so it works in that situation.
cheers Cam
Cam Cunningham

Make sure that the horns are supplied from the regulator "A" terminal which is wired directly to the brown main supply terminal on the starter switch, and NOT the "A1" terminal, which is connected to the battery via half of one of the "series coils". Its just possible that it could reduce available current a touch.
Lindsay Sampford

I have just 'attacked' the horn that I had been trying to tune on my model train transformer. I connected it up to my battery while I had it out on the bench this afternoon. Near jumped out of my skin with the noise. Tomorrow's job is to replicate Dominic's efforts (hopefully with more success)!

Any progress Dominic?

Steve
Steve Gyles

It has been fantastically sunny here, so I've been enjoying the sun instead of lying under the car in the garage. I'll have a look later in the week.
dominic clancy

Dominic,
Your comment re the bracket was interesting. For two horns you have to have a left and a right bracket as they are not the same. Was it a case of having the wrong bracket, or the right bracket with incorrect hole spacing?
Peter.
P. Tilbury

Back in the saddle after having a kidney stone removed this week, so it's going to be a few days before I get back under the car.

I know that the brackets are handed. The bracket for the chassis extension is correct for the horn and left side of the car, it was the position of the bracket on the horn itself that appears to be wrong. I just removed the bracket from the horn and spent some time with a file so that I could refit it one hole further around on the horn casing. Now it fits with the horn in the correct orientation.
dominic clancy

This thread was discussed between 21/05/2009 and 28/05/2009

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