The white (signal) wire solders to the M(motor number) on the board and the black (ground) can either be left disconnected, or soldered to a ground pad on the board. There’s some debate about whether or not you need to connect that ground wire, that’s up to you. It definitely won’t hurt anything.
I would like to take benefits of this topic, because I wondered same question. Now is clear.
I would like to ask, why there are 2 PWR port connectors in the PX4?
Can I connect a second power source and monitor through the PWR2?
PM07 A <> PWR1
PM07 B <> PWR2
I want to supply power separetly to motors and electronics, and monitor them.
Thanks.