Troubleshooting an acoustic pickup with no sound is a job that begins easily enough and becomes progressively difficult as possibilities are tested and exhausted. Fixing the problem without calling a guitar technician is not always easy, given the inherent difficulties of working on electronics installed in hollow guitars.
Check your pickup's batteries to see if it is active. Replace the current battery with a fresh one.
Plug your guitar into your amp. Verify that the amp is set to a level that you can hear, and that the cable you are using is functioning properly.
Adjust any controls on your guitar's pickup. Listen carefully for pops, clicks or hissing, which may indicate dirty or damaged controls.
Inspect your pickup's wiring using your flashlight and dental mirror. Reconnect any disconnected wires that you find. Contact a qualified guitar technician if you are not sure how to reconnect the wires.
Test the pickup's continuity--electrical conduction--with your multimeter--electrical component testing device. Zero your multimeter or set it to continuity test and place one probe at each end each wire on the pickup. Repair or replace any bad wires if you are able to do so.
Place a towel or blanket on your work surface to avoid scratching your guitar's finish.
Do not attempt any repairs on your guitar if it is still under warranty.