[TR] horns, battery poles

[Dave1massey at cs.com]

In a message dated 9/14/2008 10:00:52 AM Central Daylight Time, 
dorpaul at bellsouth.net writes: 
> My puny 12v portable battery did not have enough power to sound my TR3A's
> horns (I could, however, hear the typical
> 'scratching-needle-on-record-type-hiss').  I also had a small TR4 plastic 
> horn
> which the same battery sounded a distinct blast.  Why the difference?  Was
> this a cost saving measure that Triumph took or maybe 'electronic
> improvement'?
> 
It could be dirty contacts.

The way horns work is there is a solenoid and a set of points.  When the 
points are closed the solenoid is energized and the armature starts to move.  As 
it moves the points open.  When that happens then is the solenoid is 
de-enrgized and the points  close up again.  The cycle repeats as long as power is 
supplied.  This is know in the trade as a relaxation oscillator.

Two things can happen and cause a horn to not work.  One is adjustment.  If a 
horn is out of adjustment either the points don't close or they don't open.  
The other is dirty contacts.  If the points are dirty there will not be 
adequate current flow to pull the armature far enough to open the contacts or a 
slight movement will change the contact resistance and the the oscillation will be 
much different than desired.  Dodgey wiring can cause the same problem but I 
assume (and we know what kind of trouble that can cause) you are taking the 
wires direct to the battery.  My TR3 horne didn't work on the car but it worked 
just fine when I ran the wires direct.  (This is why a relay is a really good 
idea)

Take the lid off and clean the contacts with an emory board or some fine 
sandpaper and clean the contacts and try again.

Dave