It is located under the vertical fin, Remove the left or right cover on the tail cone above the horizontal fin for access. Starting with SN AA1A-0435 there is also a load resister attached to it.
The most common issues with the AeroFlash beacon is poor connections or grounds. The components themselves don’t fail that often. The beacon draws like 8 amps, and any high resistance in the connections (including the bulb socket) can cause it to quit working.
AeroFlash just recently closed their doors, so parts are getting hard to come by.