Only 77 and later had grounds at the horns and 12v fed from the horn button,
before that the horns were supplied with 12v from the purple fuse and the
horn button put out the ground. With a voltmeter on the purple at the horns
you should see 12v with both the horn button released and operated. If it
drops significantly with it operated then there are one or more bad
connections back through the purple fuse. If the courtesy light goes out or
dims right down when you operate the horns it is the fuse/fusebox or the
brown supply to it. With the voltmeter on the purple/black at the horns you
should see 12v with the horn button released and 0v with it operated. If
higher than 0v the problem is a bad ground back through the horn button and
column, check again at the connector by the column, the slip-ring and
contact by the wheel, and on the column shaft and housing itself. With
these last two it should show 0v all the time. If it rises with the button
pushed it is the column ground itself that is suspect, and this is quite
common with collapsible columns if that is what you have. If the column
shaft stays at 0v but the slip-ring doesn't drop to 0v then it is the horn
contact itself or one of the connections to it. Because my V8 (collapsible
column) has a bad (but consistent) column ground *and* a poor connection
through the (MotoLita) wheel I opted to use a relay between the button and
the horns and this works fine, the relay needing much less current to work
than the horns and so much less affected by bad connections.
PaulH.
----- Original Message -----
> The horn on my 71 MGB works intermittently. Sometimes it works fine and
other times it sounds like someone turned the volume down to the lowest
level.
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