limbot
36
Sadly, it’s a process of elimination to work out the issue:
- Updating the firmware to the latest, not only gives you all the new functionality in the 3.x but also eliminates the old firmware as an issue
- Resetting the device eliminates a configuration issue in the AR300m causing the problem
Once you’ve upgraded and reset do the initial setup of the AR300m ( Language and password)
Plug in your modem and setup the tethering
Plug a device into the LAN port and see if you’ve got internetz
Connect to the WiFi and see if you’ve got internetz
If you haven’t on the LAN then there’s a high certainty that there’s a fault with the LAN port assuming cable and device are fine and also the Mobley are not an issue.
I’m basically just going through the steps I’d go through to diagnose .
Hopefully between that and Jeffsf’s suggestions 
@jeffsf given how the mobley is normally powered via a car I’d assume it’s maybe 12V normally . Possible that the USB to Mobley adapter is drawing too much power for the ar300m to handle (assuming this is what @wacnstac is using) and stuffing the LAN port signalling?
" * May not be compatible with low output (mA) USB power sources like some smaller power banks or USB chargers"