I had a similar question about this a while ago. Jenna helped me out with the pin assignments. I built a cable following her instructions and it worked great. (I was also using MSport Pro software. Here's her response:
>>>>>>>>>>>>>>>>>
My previous post had the answer for wiring from a computer:
2 In (from timer)
3 Out (to scoreboard)
5 Ground (common)
You can buy a null modem adapter and just plug that in between the USB->Serial (DB9) or build a new DB9->Banana plug with the pin outs above. If you use three single banana plugs, you can use this for any situation. I keep a number of these around and it lets me plug in multiple devices in between computers, timers, and scoreboards. Either way, I still never understood why Tag put scoreboard out on pin 2.
Jenna
www.allsportsevents.com