Does the whistle tender work for sure? You haven't mentioned the type of engines (mod vs PW) .
Test ..mostly for POstwar, disconnect track power, reconnect -9v dc might do it, 12vdc should, up to about 20vdc max, should trigger the relay &run the whistle motor. 2- 6v lantern batt. in series = 12v, ( bat1+ to bat2- ; now use bat2+ for + and use bat1- for -)... 9v in series(18V) or parallel (+ to +, - to - =9v, slower drain (tests only)... a 12v car battery... or a DC power supply @ 2.5a min, hopefully 3-4a.
Running a train on dc makes the whistle or horn blow non-stop on pre/postwar and some modern ones. (I run a small loop off a car battery or battery charger by running a non whistle tender or hornless diesel; motors and e-unit don't care much and function normal (e-unit stands a slim chance at building magnetism; dissipates with ac use or running pawl thru a screwdriver demagnetizer)
This dc supply test trick may work on some modern Lionel boards too, but not all mfgs. No harm done to try, (ac contains both dc polarities naturally, doesn't always need both though). Modern andwill clang the bell if equipped depending on + or - dc wires go to center rail. PW does whistle/horn either way dc is wired to track)
