It should work with ground power, unless something broke. Here are the steps I would do:
With external electrical power -
1. Battery - ON
2. EXT PWR switch - RESET - NORMAL (right click)
3. GND PWR switches 1, 2, and 4 - B ON (left click hold for 3 seconds)
4. L® DDI, HI/MPCD, and HUD - ON
5. COMM 1, 2, and ADF - AS DESIRED
6. Warning and caution lights - TEST
7. Inertial navigation system - ENTER WAYPOINTS DESIRED