If you have a Lionel diesel with a battery-operated horn that sounds like bleating sheep, here is a tip that will give you strong, clear horn honks. The current from the horn battery must pass through the hinge joint of the horn relay’s moving armature. This joint consists of a layer of copper sheet that has the relay contact at one end, the steel armature, and the steel frame of the relay. The connection between the copper sheet and the steel frame degrades over time due to galvanic action and dirt buildup, resulting in a voltage drop across the joint that is a significant portion of the 1.5 volts available from the battery. As a result, the horn is starved, yielding unreliable and weak operation. (By the way, I have found that the relay contacts are seldom a problem since they tend to scrub themselves clean with repeated closures.)
I add a bypass wire that connects the copper sheet carrying the relay contact directly to the battery terminal. I use a few inches of flexible #24 or #26 wire with one end soldered directly to the center of the copper sheet and the other end soldered to the positive battery terminal. This bypasses both the hinge joint and the sliding joint at the battery terminal. The only trick is to make sure that the wire does not interfere with the free operation of the relay armature.
I have modified all my F3’s and Alco’s with excellent results. The strong horn honk satisfies me without the complexity of digital sound.
Whistling tenders also have this problem, but to a lesser extent because the whistle voltage is the full rail voltage. I have begun to modify my tenders, too.