I suggest you try to figure these steps out on your own cause its more fun but if you don't care here ya go:

Power + Mystery box: Find and shoot 8 unlit lanterns (a sound will play when shot) doors upstairs will open to box and a door under the stairs in fireplace room will open revealing power switch

-right of Kar98k wallbuy on stone wall
-in wagon on your way to destroyed train
-inside the main house to the right on barrel
-outside window on barrel near stairs
-outside window of kitchen on barrel
-upstairs on bookcase right of piano
-upstairs left of double doors on chair
-on top of cabinet in room with MP40 wallbuy


Pack-a-Punch: once power is on find 3 numbers on clipboards and enter them into number pad to the right of the metal gates. (they have multiple spawns)

(the clipboards will be next to corresponding colors, In the mystery box room you will find a clipboard next to a blue car, that means that number should be inputted under the blue light and so on.)