Horn problems on old lionel set

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

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

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In addition to "Geezer's" sound advice, you may have dirt buildup from a mix of oil and graphite from the motor brushes on the contacts that meet when the relay energizes. This will sometimes cause the contacts to stick together and not release when the relay is deenergized.

The check for this also clears the problem. Take a strip of paper around 1/2" wide by 8" long and slide it between the two contacts. Use a popsicle stick, or something similar, to lift the lower contact until the paper is gently caught between the two contacts. Slide the paper through the contacts while mainting this slight pressure on the paper. If there was a dirt build up on the contacts, you'll see it smudge onto the paper. Repeat on a clean area of the paper until no more grime transfers.

If the relay still sticks and you've double checked the things "Geezer" mentioned, try running the paper between the movable metal plate and bottom of the relay coil to clean out any detrious that may have accumulated there.

-- Len Head Rust Scraper KL&B Eastern Lines RR Museum

Thanks Len and Geezer, I hope that's what it is. I'm going to tackle it in the next day or two and see if I can get it working. Until then my fingers are crossed. My wife tells me our grandson is going to be mighty disappointed if we don't have a properly operating whistle.