Reply to "Bluerail and Deadrail Mod to MTH 7Premier R-2 Engineering Sample. UPDATE 10/01/21 IT'S ALIVE!"

If you have an output from the DCC decoder for the coupler that does a momentary pulse in the 1/4 second range, there's an easy way to fire the coupler.  Use that pulse to actuate a relay and use track power to fire a PS/1 or Lionel coupler through the relay contacts.  Either of these couplers will work fine with 18V as long as you don't leave it on for more than around half a second.