Yo have to dissassemble the cigarette usb regulator and solder to wire to the 5v and the gnd pin of usb connector, and simply connect them to bluetooth +- pins:
I desolder the male dsub plug (the bt adapter not work asd pass-through) and put them together in a small box.
You need to configure the BT adapter to 19200 baud, and change BT name and password, with serial terminal program.