I did a Google search for Mondo Stinger LED and the manual states: 8. Exclusive power pilot LED resolves the question of whether the transmitter is getting powerand is “on.” The LED is on only when the switching power supply is functioning. This meansthat the LED is only on when the unit is properly powered and the input voltage meets theminimum voltage requirement as set by the battery saver selection switch. (See #10below) You can find the manual at http://www.iftrontech.com/images/media/MST5.8-User-Manual-Rev-B.pdf It doesn't seem to explain why the LED would be flashing, although it suggests that there is a power supply problem...as it does suggest the LED is a simple "on when the unit has power." On the Mondo Extreme 1500 mW Tx, the data I found (well, Mrs. Google found) is: On Board LED flashes for:● Number of cells detected upon power-up.● Battery low● Temperature too high (Fan blocked, etc.)● Immanent shutdown due to catastrophic over tempSee http://www.rcgroups.com/forums/showthread.php?t=1656554 That all said, you might want to contact IftronTech at http://www.iftrontech.com/contact_us.php (or just email to email@example.com). They've been very responsive to me when I've emailed (my contact was Ira Faberman, but that was back in 2013 so I'm not sure he's still there). Hope this helps. Andy.