1.When placing the DC meters selector (on the AC/DC metering panel) to BAT BUS or STBY PWR, why is the amperage indication blank (no value) and only voltage indication shows. Why no amperage? Is there no current flow to the equipments concerned from BAT BUS?
When are you testing the voltage/current in this situation? What power source is on the aircraft?
I had a look at the wiring schematics, but after following wires on a dozen pages, I was none-the-wiser. Which airplane, exactly, are you talking about? 737 Classic? 737NG?
Regarding the Caution light, (EDIT), on the NG wiring schematic 24-31-11, a wire is shown going from the APU ECU to the P5 (overhead) panel. When the APU is started, a signal on this wire stops the CAUTION ouput from the panel.