What does it mean on an MNL-800 if both the top green LED (Transmit) and the Amber LED (Receive) are on continuously?
MNL-800, MNL-200, MNL-100, MNL-50, MNL-V1R, MNL-V2R, MNL-V3R
LEDs indicate LON traffic on the trunk
For an explanation of the Transmit (Green LED) and Receive (Red LED) see F-26724, MNL-800 Installation Instructions,
If the amber LED is blinking fast enough, it appears to be ON continuously, so it's receiving data at a high frequency.
The other MNL devices on the same LON should all be behaving the same way, indicating a lot of LON traffic.
Confirm with a LON protocol analyzer.
If excessive LON communications traffic is suspected, see Lessons Learned Article #3366 for a method of throttling LON traffic.