For the AMX240 to transition to Day Mode or Full Bright Mode observe the following:

When the aircraft dimmer is turned to minimum (or off) the lighting will automatically go to full bright.

The AMX240 at 0 VDC, the lamps are full bright. At 1.2 VDC, the lights transition to night, and are dim based on rheostat setting. 

If the Dimmer is set to minimum and the AMX240 is not transitioning to full bright, then it is likely that the dimming module is outputting more than 1.2 VDC causing the AMX240 to stay in night or dim mode. 

This can be verified by pulling the dimming module circuit breaker and observing the AMX240 transitioning to full bright or day mode. 

Bench Test Example