I have been trying to use a DB9 switch box to switch the Legacy Base DB9 from the LCS DB9 to the computer LSU DB9 serial input. When I connected everything, the LCS no longer functioned correctly...blinking red lights. I found that this happens if the computer case ground is connected to the LCS DB9 metal shell thru my switch box. Various possible reasons...but no matter, the fix was to not connect the shells together electrically.
So I made up a jumper cable from the computer DB9 with a plastic shell to plug into the switch box. And it all works now...can switch from A (LCS) to B (LSU) with the switch box (turning off the LCS power first just to be safe).
Just an FYI if anyone runs into this...