I don't think a wide band will work correctly on a 6 volt circuit. An 02 sensor is basically just a resistor that provides a signal back to an ECM. If you only have half the voltage going in, you wont't have the correct signal current. A wide band also has a heater circuit built into it, so 6 volts won't cut it. Just food for thought, I've used a 14 volt cordless drill battery for bench testing, you may be able to rig something up to use for tuning purposes.
