Regurgitated from Indigo's support site.

The MorningLinc controller uses RF to control locks and deadbolts from Morning Industries (now known as MiLocks). Because the RF communication is one-way, there is no status presented from the lock to the MorningLinc, so Indigo can't know the status of the lock (locked or unlocked). The controller has an additional INSTEON security feature which requires special linking steps. Specifically, you must use the technique of holding the MorningLinc's SET button when defining it and not try entering the INSTEON address directly into Indigo.

To define the MorningLinc device in Indigo: Select the File→New Device… menu item to create a new Indigo device. Press the Define and Sync… button inside the device dialog. Press and hold the SET button on the MorningLinc module itself. The INSTEON address should automatically fill in to the Define and Sync dialog. If it does not, then try plugging the MorningLinc into the same outlet / circuit as the PowerLinc. Press the Start button.

Indigo should now start the linking process. If Indigo is unable to communicate with the MorningLinc RF, then again press and hold the SET button on the MorningLinc for 3 or 4 seconds. That will complete the process of defining an Indigo Device for the MorningLinc. However, the MorningLinc does not appear to respond to direct Turn On and Turn Off commands from Indigo. Instead you must create individual PowerLinc links to the Morninglinc (1 for lock and 1 for unlock): Select Manage INSTEON PowerLinc Links from the Interface menu. Select an unused PowerLinc Group/Scene number from the popup, and optionally give it a name such as “MorningLinc Unlock.” Select your MorningLinc device from the popup toward the bottom beside the word responder. A sheet will drop down, explaining that you can't remotely program the MorningLinc, but that the PowerLinc is now in linking mode. Single tap the MorningLinc SET button to get it into the desired lock/unlock state. Press and hold the MorningLinc SET button for 3 seconds. Press the Finished button in the drop down sheet. You must next repeat the steps above for the other lock/unlock state. You'll want to select a different PowerLinc Group/Scene from the popup (step #2), and you'll want to put the MorningLinc into the opposite lock/unlock state for step #4. Addendum:

We've had reports of successfully reusing the same PowerLinc Group/Scene for the unlock state. Apparently the trick is to put the MorningLinc into the unlocked state then double tap (instead of single tap) the SET button before holding it down for 3 seconds. That's it. You can now use the 2 PowerLinc Scenes (or single PowerLinc Scene if you followed the modified addendum notes) to send commands to the MorningLinc to unlock and lock it.