lambda sensors, wiring and cats

HI can anyone help me with first of all lambda sensor wiring on a 2000 v8 discovery, on the computer it says the heater system is not working on either side and no reading from left side sensor, there are 4 wires at the plug, ive got ignition live, the orange/white wire is the ecu control earth which also reads battery voltage with ignition on and drops to 2 volts with the engine running, i think the other 2 wires are the read wires for the sensor, ive removed the sensor and if i put the 2 black wires across the battery it heats up, but there is a resistor in the wire, the one black wire goes to the one side and the other black wire goes on other side, i can not see how the sensor gets an earth to heat it up, the car also stinks of rotten eggs, the car is very flat as it starts to warm up, but if you can hold some revs on it seems ok until you get to about 60 mph then it starts getting jumpy, at lower revs you can here it popping down the exhaust on the left side, could it be the cat as been damaged,
thanks phil