constant horn with conventional operation

What transformer are you using?

z4000

I have the same issue with one of my Williams engines.  The horn blows constantly when running on track powered by Lionel CW-80 and GW-180 transformers, but it runs fine on my track powered by an MTH Z1000.

Ron

It could be some resistance in the power delivery causing a DC offset. Since it is only impacting one locomotive, let us first look at the locomotive, but dirty track can also be a cause. I would clean the wheels with IPA or GooGone and the center pick up rollers with CRC 2-26 or Deoxit and see if that helps.

Probably a wire that is carrying DC is shorted to the frame and AC ground.  This induces a dc offset causing the horn.  Certainly, could be a defective sound board, but I have not run into that.  Check internal wiring especially motor leads and solder joints.  G

I'm inclined to think that my problem is caused by a wire shorted to the frame or a sound board problem.  Engine and track are clean, and the engine did this right out of the box.  I'll open the engine and check the wiring.  Thanks for the tip.

Ron

Be a couple of days before i can test again, although it too is new engine and the track is not giving any other engines trouble.