Subject: [TR] TR4 Finally tooting my own HORN, Triumph days of MUTE are over.

From: "Will Daehler" <[email-masked]>
Date: Wed, 3 Apr 2013 16:09:59 -0400

Last fall I started trouble shooting my TR4 horn circuit to see why I wasn't
getting anything more that brief inaudible chip.

At that time I did post a request for help, and did get four excellent
responses from this list.  I investigated and tried all the suggestions,
still to no avail.  The more I measured voltage drops, resistances and
currents, the more it seemed that the OEM circuit design itself was flawed.
Just feeble. Pardon my criticism, Sir John Black.

A relay was needed!

So I lashed up some jumpers and was able to put in a trial relay without
cutting any wires in the existing harness. On this first attempt, the horn
personality changed. Now instead of one tiny peep, I got a whole series of
rapid fire little peeps.  Yes, the coil in the relay was chattering. I was
close, but gave it some more thought for another month.

I  sketched up a better way to connect the relay so that there was more
complete separation of the coil signal circuit and the contact power
circuit.  Then I worked on reducing it into the easiest possible
implementation, meaning cutting no existing wires, just adding jumpers with
the correct crimped connectors.

It worked !

Absolutely amazingly loud ....HOOOOOOOT !

A picture right now would help, but here comes a thousand words instead.
The OEM circuit has a P (purple wire) and a PB (purple wire with a black
strip).  At the site of the driver's side horn, I mounted the relay
underneath the little sheet metal stand that the horn is mounted to.  So its
hidden from view. 

To the extra tab connector on the P side of the horn, I ran a jumper wire to
one side of the relay coil. From the other side of the relay coil, I ran a
wire through the firewall and underneath the dash. There I found the little
three way connection point where the three PB wires meet.  I unplugged the
one going to the steering column, and connected it to this new wire coming
feeding from the relay coil.  So here we now had a signal path that when the
horn pushbutton in the steering wheel was pushed, this completed the P
circuit to ground.  The load on the P circuit was the coil. (No blue Lucas
smoke).   

That left how to hook up the power circuit, which was connecting the PB tab
on the driver's side horn to the first side of the relay contact, and then
another jumper from the other side of the relay contact to ground. When the
coil is energized by the signal circuit, the contact closes, and the
electricity rushes unimpeded through the horns across the contacts and
straight to ground.

Elegant.

Faithfully submitted,

Will Daehler

** [email-masked] **

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