Does anyone happen to know what the polarity in the H&K subwoofer is on my 2013 ML63?

I’ve searched and haven’t been able to come up with anything. I’m adding a high low converter and need to know the polarity of the 4 wires. There is 1 red 1 black on one side of the speaker and 1 green 1 gray on the other side of it.

i don’t want to resort to the battery test if I can find the actual wiring schematic. Any help is appreciated.

 

Incase anyone is wondering, in this case with this dual voice coil sub, the smaller of the two terminals is the positive +. So the red and the white.