Replacing gen 5 (n) extreme with gen 6 (ac) The new one continues to flash amber.

Suggest that you find out why the amber light is flashing.

Assuming that you have recent model Mac.......Open Macintosh HD > Applications > Utilities > AirPort Utility

Click on the amber dot

Another window will open

If you see an Update button, click it. The light was flashing to tell you an update was available.

Otherwise, look at the setting for Status and click on the small amber dot there. Report on the message that you see.