Voltage flows through the Keyswitch; if it is old, has not been replaced in a long time, there will be high resistance within the Keyswitch & that will decrease voltage to the BDI.
I suggest that you install a new Keyswitch, then watch the BDI after you close Keyswitch.
The batteries could be very weak, very old & might need to be replaced.
The maintenance free batteries that crown installs in the WAV only last about 3 years.
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