1. The gyroscopes in the gyro instruments are not electric, but are spun up by air being blown over paddles moulded in the sides of gyro. This air is provided by a suction pump - and the gauge tells you that pump is working properly (and you can thus trust your gyro instruments.)
2. The HTR OVER TEMP light tells you that the cabin heater is over temping. LO BUS I would assume is a bus under voltage.
3. Need a bit more of a hint!!