However if the LED's should light up when I turn on the master switch I must have a problem. Everything else is working so the AT module should have power when I turn the master switch on. So the LED will light up even if the unit is not on? Everything in the boat is hooked up to a 12 socket fuse block that powered up by a master power switch. I'm not familiar with the Elite FS, so must ask do you need to enable the hard wired Ethernet port? If that LED isn't blinking, your MFD isn't communicating with the AT module. The Ethernet LED should be blinking on and off to indicate activity. (If I recall correctly, solid green means booting, not 'up and running'.) The amber/green alternating indicates the unit booted and is operational. The 'normal' state for the Power LED is to alternately blink amber and green. For instance: Look at the module to see what the indicator LEDs are doing. When you say 'the AT box has power' explain exactly how you have determined this.

That error is corrected in the AT module release 20.1-64.2.66 that occurred about 4/24/21. So, your unit never powering up is NOT an indication of the software error that existed. In other words, you could turn it ON, but there was no way to turn it OFF - unless you had a switch to interrupt the red power wire going to the AT module. However, ONCE IT IS ON, turning the voltage OFF on the yellow wire would not result in the AT module turning off. Lowrance confirmed in videos produced by the company that the issue was/is as follows: When the MFD turns on, the yellow wire WILL turn on the AT module. As an input, that 12V on the yellow wire will cause an accessory to power up if that accessory's red/black wires are connected to an active power source (your fuse block in this case). Anytime an MFD is on, it's yellow wire (output) has 12V on it. It's an output from your FS unit, and an input to the AT module. Yes, the yellow wire is a 'trigger' or 'wake up' wire, think like remote on/off switch. The AT box has power but no way to turn it on. My understanding is that the yellow wire is like the on off switch. Yes it has power directly from the fuse block that is turned on at the master power switch.

Lowrance active target software update