Modify M4 Tracer Magazine (Tan - 150 Rounds) & 1200 Big Foot 0.20g Tracer BB's M4 Bottle

Step 1 : Install the Battery

Loosen the screw from the LED box to remove the battery cover plate.
Install the attached three mercury batteries as shown.
Fasten the cover plate with the screw.
Caution:

Make sure the + and - battery contacts are properly oriented. The LED may not work when old and new batteries are used together.
Make sure no BBs before disassenbling magazine.
 

Step 2 : Install the LED box

Loosen the screw to remove the bottom cover from the magazine.
Take out the magazine inner case from the magazine cover.
Install the LED box into the magazine inner case.
Fasten the LED box with the black screw.
Assemble the magazine and tighten the screw to finish.