The only connection to the battery should be to the BP35.
There are options for fitting items directly, depending on which setup you have.
When you have a BP35-II you will need to connect the positive line to the BRK line of the BP35 with a suitably rated fuse. You should find a line of 4 fuse holders connected to this near your BP35-II. This is your line out point for heaters, breakaway systems, sway controllers and the like.
The grounding is to be done to the chassis or directly to the battery, whichever can make the best connection.
If power is taken directly from the battery, the system cannot monitor the draw. This will lead to your display showing incorrect figures and may affect your charge algorithms. In order to wire to your battery directly, you will need to use a BC300 and Commlink. Please refer to "How do I install a BC300 to my system?" for more information.
BP35 range (mk1)
When connecting to a BP35 mk1 system, if a device or appliance using less than 15 amps is being fit, the positive connections can be made at the battery (using a sufficiently rated fuse).
The grounding must be taken to the BP35. This can be done by directly wiring to one of the negative pins or, if the BP35 is earthed as recommended to the chassis, you can connect the negative to the chassis, allowing the BP35’s chassis ground to return the current.
When making additions to a Genius-II system, you can take your positive line directly from the battery, with a suitably rated fuse.
Your grounding can be to the battery if you have no monitoring systems. If you have a Drifter or a similarly styled battery monitor, you will need to connect the ground line to the load side of the monitoring shunt. Failure to do so will prevent the monitor from seeing the power usage and it will give you incorrect information.