First, disconnect all wires from the transformer itself and plug it in. Turn it up and listen for the circuit breaker. If the breaker trips with no wires and no trains hooked up, then there is a problem with the transformer itself, and it needs to be serviced.

If the transformer checks OK, then hook up the wires to the transformer and a lockon. Connect the lockon to 1 section of track, and turn on the transformer again. The transformer should not trip. If it does not trip, put a lighted car on the track if you have one. The light should come on. If you have no lighted car, try the engine, holding it to keep it from rolling. You just want to confirm the transformer, wiring, and lockon are OK and giving power to 1 section of track. When this test is passed, turn off the transformer, remove the car or loco, add 1 section of track, turn the transformer on, put the loco on the track again, turn on the transformer and check for power again.

Continue adding 1 section of track at a time and checking for power with a car or engine. If the breaker trips, the last section of track added is bad.

Larry