FBL2360 grounding question

In the FBL23xx datasheet we are cautioned (note 6 page 5) against connecting the ground pins of the 25-pin connector to the negative battery terminal. But in order for the controller to use DOUT3 (pin 19) to control a contactor whose coil is connected to the positive battery terminal the controller must connect DOUT3 to the negative battery terminal. Will this feature operate properly even if there is no connection of the I/O ground pins to the negative battery terminal?

Is the reason for this caution simply to prevent large current from flowing through the I/O pins?

Thanks

I see the diagram and understand it well, I think. What I am really asking is this:

Why are we cautioned against connecting the ground pins of the I/O connector to the battery minus? Aren't they connected together inside the controller?

Thanks

Scott

One example of a problem that connecting battery - to the sub-D: if you attempt to run a motor before the heavy B- wire is connected, all of the current will flow through that connector and might well destroy it or a trace on the board.