ELK M1 Gold and TG-1 Express wiring


I am looking at the TG1 wiring diagram specifically for the Elk M1 Gold.
It suggests a CAT 6 wire and 1 more conductor for the TRIP IN.
Where I want to put the TG1 is right next to a ELK-M1XRF2H which currently has a dedicated CAT 6 cable but the blue pair is not being used. Can I use that blue pair for the TRIP IN?
Also, do I have to use OUT 3 on the m1 gold?
You could use the spare pair for the TRIPIN signal.  But  I wouldn't recommend mounting the TG-1 right next to the M1XRF2H.  That risks RF interference between the two units.  Better to mount the TG-1 at least several feet away, further if possible.
You could use the OUT3 relay on the M1 to activate the TRIPIN input, if you're not already using it for something else.  But any other relay connected to TRIPIN would be fine, too, such as an Elk 912, controlled by, say an M1 voltage output.