Hmmm... for that sort of situation my first instinct would be to use sync'ed waypoints (F5 and drag a blue line connecting) rather than triggers... however both would work.
To set up your trigger, group it (F2 and drag a line between the trigger and the unit) with the unit you want to set it off. You'll get some new options in the 'present' dropbox. If you set it to
Group Leader Present that trigger will activate when the group moves through it.
Now what you want to do is have group
es1 with a HOLD waypoint. Then sync your switch type trigger with that HOLD waypoint. They will move on to the waypoint
after the HOLD when your first group moves though the trigger....
Hope that's coherent enough to help solve your problem