So make those junction box things a blueprint, ie they are all copies of the same blueprint. Give the BP a variable ‘chess piece’.
Then, either from the level BP or a ‘manager actor’ you can set the variables on the junction boxes to a random combination.
If the piece the player tries to locate is the same as the variable on the junction box, they are allowed to place it.
( or you can compare them after they pull a large switch etc… )