What I have found from a source that I trust is that the Greenstar and the Insight both only need the recieve pins hooked up to the send pin at the gps source. In other words instead of 2-3, 3-2 and 5-5 (ground) that is used for a normal null modem hookup only need 5-5 and 3-2 hooked up. This eliminates any possibility of either the Insight or Greenstar from sending information back and confusing the other unit. In other words both Insite and Greenstar can only "listen" and the gps can only "send" with just the two wires hooked up. Two way communications between the gps and consoles are not needed.

I have made cables up before but think I am going to have Ted at L & D Ag do it 1. because he knows what he is doing and 2. he does such a neater and more professional job than me. He is shipping us some other cables anyway. 

John