Dan, all,
Thanks for your assistance. I tried posting a reply to Joe Curry to the list,
but it never showed up. Joe gets the prize for figuring this perplexing
problem out. Details and photos of the culprit, including schematic can be
found here:
http://www.totallytriumph.net/cgi-bin/dcforum/dcboard.cgi?az=read_count&om=16
0&forum=DCForumID5
Turns out, these replacement relays by Lucas, which are supposed to be direct
replacements to the original horn relays, are not. They do not give good
instructions, and they also require a positive 12v feed to TWO terminals on
the relay, instead of just one, which is all we get off the wiring harness for
the horn relay. This means I have to fashion a "Y" out of a short length of
wire with connectors to split the 12v source across the two leads that
requires it. One activates the relay solenoid, the other supplies the voltage
to the horns. It's a goofy setup. But at least the horns will work. Time to
heat up the soldering iron.
Take care,
Jeff in San Diego
1968 Spitfire Mk3 aka "Mrs. Jones"
1970 GT6+ aka "gnarly project"
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----- Original Message -----
From: Dan Canaan
To: spitfires@autox.team.net
Sent: Thursday, March 20, 2003 11:41 AM
Subject: Re: Calling all electricians...
Does the relay click when you supply 12 vdc and ground from the battery
with test leads? Will this cause the horn to blow?
No: Check polarity of relay. Some are polarized with a small diode inside
to prevent damage by a collapsing magnetic field when the relay's coil is
released. The case should be stamped with the connections. Try again with
reversed leads.
Yes: Great! The relay is good, as is your wiring to the horns. We just
need to get the relay to work from the wires attached to the car- they
always work on the bench but Lucas lives on. If the relay works with 12
vdc applied with the test leads, reconnect the horn to the harness and try
only jumping a wire from the positive battery terminal to the positive
terminal on the relay.
Hit the horn button. Does it work?
No: The relay is not receiving the switched ground current from the horn
button. That passes from the front of the chassis to the steering rack via
a small flexible strip on top of the grease nipple of the steering
box. The current passes through this column to a sliding joint with
another flexible strip. On up to the center of the steering column to the
switch. With a test light connected to a good known source of constant 12
vdc, touch the horn contacts in the steering wheel. If test light lights
up with the contacts closed, then you know the ground path from chassis to
that point is good. That's the hardest part. Follow the lead as it exits
the steering column under the dash and continues to the horn relay
itself. Keep testing it at various points to make sure the current flows
when you hit that horn button all the way to the terminals on the relay.
Yes: You're not getting a constant 12 vdc to the relay. While you could
bypass that with your own wiring, it's better to go back from the relay
through the harness and find out where it is no longer making contact.
Having a couple of 8 foot lengths of test lead works wonders for bypassing
issues while testing. It's cheap and very easy to make from wire and
alligator clips.
-Vegaman Dan
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