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MG MGB Technical - horn on 1974 MGB

horn quit working on my 1974 MGB. Confirmed that 12 V is present at horn using voltmeter. Tested horn by jumpering it directly to battery -- and it works. Removed 'horn switch' at steering wheel -- and the spring-loaded contact seems to be fine. Anybody else ever have this issue????????
THANX!!!!!
Barbara Rousselle

There is a very comprehensive Horn diagnostic at this website:
http://www.mgb-stuff.org.uk/rideframe.htm
You may need to follow the links to go to electrics, then to horn, but it is what you need.
R Hill

There has been plenty of traffic about horns. You may want to check the archives.

The horns are a pretty simple system. From what you've described, I would try slight adjustments to the horns to see if you can coax them into sounding. There is a small adjusting nut on each horn. The adjustment supposedly alters the pitch. However, seems like most people fiddle with it and become quite excited when their horns simply come to life once again. Put me into the "happy days again" category.
Brad Batchelor

If you try to adjust the horns as Brad suggested, remember that the threads on the adjustment bolt unscrew clockwise. They are reversed.
Robert Browning

The horns on my 72B didn't work and I did the following to fix the problem.

There is a copper/brass ring on the back of the steering wheel that makes the electrical contact to the spring loaded assembly that passes through the steering wheel. I cleaned/polished this ring with steel wool (this required removing the plastic cowling around the steering column, which for me is best accomplished by removing the three bolts holding the steering column in place and dropping it).

When you remove the steering column cowling you will find a springy piece of copper behind the wiper switch that brings power from the wiring harness to the copper ring mentioned above. It is actually attached to the turn signal switch, but it does not need to be removed. Take a piece of fine grit (200+) sandpaper, and run it between this contact and the copper ring three or four times(grit surface facing the dash board to clean the contact). Be careful that you do not bend this piece so that it no longer makes contact with the ring on the steering wheel. Before re-mounting the steering column make sure the two parts described above still make contact, and then try pressing the horn button to see if your horn now works.

This fixed my problem. I hope yours is as easy to fix.
Greg

DON'T try adjusting the horns until you have ascertained that it really is them that are at fault and not an electrical connection. If they were working and don't now, and both horns went out at the same time, then I suggest it is an electrical problem and not a mechanical adjustment one! The horns need a good voltage supply and good connections or they won't work properly. Tweaking the horn may get round a bad connection elsewhere, but that really isn't the best way to fix it, and it still won't give as good an output as fixing the real problem will.

Checking for 12v at the purple at the horns (go right on the spade and not just the wiring connector) is a good start, but you need to make the same measurement when someone is pushing the button. If the voltage drops appreciably - and it could go all the way down to zero - then the likely cause is corrosion at the purple fuse or its connections in the fusebox. Then do the same test with the voltmeter connected to the purple/black spade of the horns. This time you should see 12v with the horn button released, but it *should* drop to zero with the button pushed. If it doesn't go as far as zero then there is a bad ground coming from the steering column through the horn switch and the wiring. Check again at the purple/black at the contact that is fixed to the column and slides on the ring on the back of the wheel as it turns, and again on the steel staft the wheel is bolted to. That will tell you if it is the wiring, horn push, or column ground. In my case it was partly due to a bad ground on the column, which is quite common on collapsible units, and a worse connection inside the motolita wheel. I opted to fit a relay as there was a fair chance of permanently damaging the wheel by trying to get at the switch, and fixing the column ground on its own wasn't enough.
Paul Hunt

This thread was discussed between 10/08/2004 and 11/08/2004

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