unfortunately, Bendix king technical spec need minimum 13.5 volt with 7 amp, and 27.5 volt with 4 amp.

the problem lay on aircraft, not enough electrical power. default Piper J3Cub has no electricity and Maule 260C only have 12 volt.
aircraft.cfg section [electrical], set max_battery_voltage = 24.0

we need your panel.cfg configuration

please, turn it on.

such weird, I have installed that radio without that aircraft you mention.
let me check.

can you give a screen capture for the issue?

did you install Microsoft visual studio C++ redistributable 2015 or 2017 package?

due to it in VC, you must contact to aircraft developer. the lit gauge are need correct material/texture setup in the model

we just provide basic item for other developer, so with that they could customize to fit with certain aircraft and get as real as it can get.

make sure custom gauge not over other gauge.

please make correct setting in configurator.
NAV1 and NAV2 need to set to which radio would be use.