Start with turning all switches in the off position.
Reset the CB and turn master (BAT) on.
If the CB trips, you have a short to the ground in the circuit.
Start removing the GND connector from each lamp and reset CB until it no longer trips. Then you know which lamp that caused the problem.
If the CB does not trip when you turn the master on, start turning on one switch at a time until CB trips.
Then you know which lamp that caused the problem.
Good luck.