The BT-105 has 4 ports and you can access all the ports by splitting the channels or by creating unique cables to do so.
The port numbers are marked on the bottom of the BT-105. Ports 1 and 2 are closest to the switch and ports 3 and 4 are located next to the USB charger. Each jack is a 3.5mm (1/8”) stereo jack.
To access each port individually you make a cable by wiring a stereo plug to your switch. A stereo plug can be purchased from AirTurn, Radio Shack or Parts Express. Look for a 3.5mm stereo plug.
Tip(L or 1 in the illustration) and Sleeve (ground or 3 in the illustration) are wired to the switch if you wish to access port 1 or 3.
Ring(R or 2 in the illustration) and Sleeve (ground or 3 in the illustration) are wired to the switch if you wish to access port 2 or 4.
The ground is the longest connector while usually the tip come up through the center of the plug.
After soldering the wires onto the plug, be sure there are no contacts touching.
Using a stereo to mono splitter you can reach all four ports. These are available from Radio Shack and AirTurn. You can use the stereo cable design for port 1 and 3 for all four ports when the splitter is used. You can also use mono cables when the cable splitter is used.