from what ive read about the thunderbox it has 3 modes, yes the white wire is for turning the accessories on when the ignition is on, and its fine to operate without it as you are, but they say if you have a battery maintenance charger you connect then you have to effectively shut the thunderbox down by connecting the white wire to the ground block on the box itself..
The ThunderBox can operate in three different modes. Depending of the connection of the
WHITE control wire the following modes can be acquired:
› Automatic mode:
The White control wire is left disconnected/unused.
When the engine is started and runs evenly, the TB switches the power outputs ON.
When the engine is stopped, after a few seconds the TB switches the outputs OFF.
› Ignition-controlled mode:
The White control wire is connected to an ignition key switched +12V power source, e.g.
to the hot wire of the number plate light or running light.
The TB will switch the outputs ON/OFF (with a few seconds delay) following the ignition
key switch position. This mode is recommended if you intend to connect a battery charger
without disconnecting/removing the battery from the bike.
› Stay-off mode:
The White control wire is connected to the TB’s Black wire terminal block.
The TB will keep the outputs OFF. If you normally use the Automatic mode, connect the
White wire to the Black (you may do so via a switch), before connecting a battery charger.
So what I am aiming to do is the stay off mode, although having read this i am a little confused between automatic and stay off as they both mention battery chargers!!!