Horn in Lionel 2023 UP alco

Postwar guys can correct me but I seem to remember a dark red fiber insulating washer that needs to go in the mix under the relay.  Again, this forum has some great postwar guys and they will jump in and give you stronger information.

The relay is screwed directly to the battery bracket.
The relay is slightly different than a whistle relay in that one end of the coil winding is attached to a solder lug instead of being attached to the relay frame.
When the battery bracket is mounted to the chassis, there should be a thin fiberboard insulating paper between the relay and the chassis. One screw should have a shoulder washer. the other screw should go through the solder lug (mentioned above), then through a shoulder washer, and then the bracket.

So, the battery bracket should be insulated from the chassis, but the relay is still grounded through the screw.

(Those shoulder washers were often red)

Thank you for your reponse.  That appears to be how it is set up.  But it still cuts out the horn when the coil is grounded throught the screw.   I even grounded it elsewhere so this would not be an issue.  But same problem.  It doesn't make sense to me!

We can figure this out. If the coil stays energized the battery is powering the relay. Check as mentioned already each of the 2 screws holding the battery bracket has a shouldered fiber washer, and there is a insulating piece of fishpaper under the battery bracket. After that is confirmed, look closely at the lower solder lug that the ground wire is connected to and it is not touching the battery bracket. Check the bare ground wire is not touching the second solder lug on the bottom of the solder lug stack. The ground wire needs to be the first wire on the stack, looking at it head on. Is the screw holding the solder lug / insulator stack the original one? If the screw has been replaced, check to see if it is too long and punctured the paper insulation wrapped around the coil, the screw will ground the coil to the frame. Sloppy soldering on the terminals on the solder lugs. check to see if any solder has bridged two lugs together. Also check carefully that two lugs are not bent and touching another, (look closely at the bottom lugs). Check that the 2 wires coming out of the relay coil are insulated and not touching the battery bracket.

It's got to be one of those items. Good luck!

He could be using a whistle relay, not a horn relay.

Update.  I have made sure that the bracket is isolated from the frame.  If I disconnect the wire from the e unit to the solenoid, I can manually move the solenoid and the horn blows as it should.  When I connect the hot wire to the solenoid, I lose my voltage from the battery.  It must be a direct short, because the battery heats up fairly quickly.  Any ideas?

I wonder whether you have the wires connected properly at the horn relay.

There are a total of three terminals on a horn relay

The closest to the frame is the terminal that goes to the horn. This should be the contact that runs down to the bottom
The next two terminals should be connected to the relay coil.
Make certain that neither terminal has any continuity to the relay frame.
One of these terminals should connect to the e-unit power terminal.
The remaining terminal should connect to that solder lug.
The battery holder & relay should be isolated from the frame.

Here is a link to the first official Lionel service manual page.
Take a look.
Thanks to Olsen's for providing a free online copy of the manual.

Thanks guys.  It's fixed

I should explain.  I fixed it with all of your help.  Someone had rewired the coil and wrapped it around the frame of the solenoid and soldered it in place.  It looked like a Lionel job, but what it did was make a direct short through the battery.  I really appreciate all of the help you guys gave me on this one.  It really wasn't tough, but I wouldn't have spotted it without you.  Thanks again.