In an earlier post I suggested where I would start. That is, the zener bias diode, the metering resistors, and I'm going to add the standby operate relay contacts. Take a look at those circuits. When in standby the relay connects the full bias, shorting out the resistor. When in operate the resistor feeds the zener diode and the resistor to ground in the meter ckt. I think that's a 68 ohm? Understand the circuit and you'll know what to look at.