Is this a new issue, or just suddenly started?
Have you recently added any new hardware…like the Bravo for example. As the Bravos default settings have the switches that will conflict with the Alpha.
In the controls menu in MSFS, on the left under search, search 13 and 14 and check they are only bound to what you want, I think 13 should be “set alternator” and 14 empty? Can’t be toggles as its not a toggle switch.
If that still doesn’t work out, go through every peripheral and see if any thing else is set to alternator. Shouldn’t matter unless something else with an always on switch is bound also…don’t leave out the keyboard. I just looked, there are default bindings for the alt. It take two keys and the chance of them both being stuck are unlikely, but, worth checking.