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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