Dale says:

Shorts can occur in many ways. I’d start by taking everything off the tracks and visually inspect every inch (centimeter?) to see if anything may be touching where it shouldn’t be. Next, I’d look carefully at the wiring making sure that no wires are touching where they shouldn’t be. Then I’d use an Ohm meter between the rails to see if it detects a short.

Lastly, if the meter does not show a short, I’d put my smallest, simplest loco on the track and see if it responds to the cab control. Then start replacing items on the track.

If you did any work on the layout since the last time trains ran, I’d focus on that area. Shorts are insidious and often difficult to locate. All it takes is an errant whisker of wire from a connection of stranded wire.

Ralph F says:

I would check the voltage throughout your layout and make sure it hasn’t changed. It is probably a loose jointer or a bad piece of track.