Relays
Some basics might help. An electromechanical relay is a coil of wire around a magnetic (iron) core, and a magnetic armature that moves one or more electrical contacts when the coil is energized.
A typical 28 volt DC relay needs at least 18 to 20 volts DC applied to its coil in order to operate. There is no way any radio frequency signal short of a lightning hit will operate or release the relay directly.
Here's the fine print part: relays often have a diode wired across their coils for the purpose of suppressing the high voltage pulse that the coil generates when you suddenly de-energize it. Depending on the speed of this diode, and the topology of related circuits, the diode could turn RF energy induced into the wiring to the coil into enough DC to operate the relay, or drop it out if it is already energized.
The problem is that you would have to induce some 20 volts of stray RF directly into the relay coil wiring, for a significant period of time, for this scenario to work. This RF would have to penetrate both the acft metal hull and any shielding on the wires. I have no idea how much RF power would have to be delivered to the outside of the hull, but my guess is it would be upwards of tens of kilowatts. This massive amount of RF power would probably disrupt other electronics in the acft long before it acted directly on any relay.
(DC = direct current, RF = radio frequency energy)