Model Forum / General / Railroads / November 2004

The most likely cause in binding of the moving armature plate at the bottom
of the horn relay.  This is the rectangular piece of steel about 3/4" wide
by 1" long with a copper contact strip riveted onto it.  It must move up and
down very freely.  Make sure the contact end of the copper strip is not
bent, and moves freely in its vertical guide slot.  Make sure the pivot end
of the armature plate is not binding.  There should be two very small tabs
of copper bent up on the sides on the armature plate to position it so the
plate moves freely. You may need to adjust these slightly to allow free
movement.

If you have a voltmeter, Lionel's specs for the horn relay are that it
should pick up on 1.1 v dc, and remain closed on as low as 0.5 v dc in the
presence of 10 v ac.  The relay should not pick up on up to 28 v ac with no
dc present.  As a simple way to test the relay, use an ordinary, not too
fresh flashlight battery - one cell should pick up the relay, and it should
drop out when the battery is removed.

While a less likely cause, the problem could be in your transformer.  If the
contacts on the "whistle" switch are bent, or the return spring is weak, it
may be turning on the 1.1 v dc horn pick-up voltage, but then not turning
off the lower 0.5 v dc horn holding voltage when the "whistle" switch is
released.  The best way to be sure this is not the problem is to use the
transformer on another horn or whistle equipped locomotive and see if it
operates correctly.

If the relay does not perform properly, it may need to be replaced.  Parts
sources like www.georgetebolt.com have replacement whistle relays (the same
relay is used for horns).  Let me know what loco model number you have and I
can tell you the correct part number.  Gary Q