There are many posts but not in changing out relay.
And. What about hijacking. A post?. If I can't. Find what I'm looking for. I'll make my own.
Now. The horn.
Stan or John should know if a PC dc relay will work.
If 5 volts dc goes thru the rails in theory it should work.
A friend with a Lionel tester ..has been under the weather. Or I would the relay tested.
I will recheck the points.
In one of the posts some solder a jumper wire.