Tripac evo problems charging, varied or no voltage

Tripac Evo No alternator light or warning triangle lights to the three knob controller.

APU giving out strange voltage readings. The inverter is reading from 13.3 down to seemingly no volts being output. My first thought was the alternater but is it normal to not be throwing codes and to have the voltage variation?

 

Thanks. It has corrosion in one of the terminals. Going to swap it out and cross my fingers.

 

Unfortunately swapping that plug out didn't work. If I put the positive side of multimeter on the output and the negative on the frame or another ground would that tell me if the alternater is putting out the the 14+ it's supposed to? I know nothing about electrical.

 

Put in a new alternator in and plugged it all in correctly. Still can't get it to show a charge any different than the batteries are. The charge isn't changing at all now though. It's all running but not showing any charge at all instead of varying like it was before.

 

I turned on the APU on and it was running. I turned the multimeter to "20" and put the red on the alternators output and the black on a ground. It showed about 12.3ish, which is the same as the truck batteries are no matter if the APU is running or not. Then I did the same thing on the truck batteries just to make sure and got the same 12.3 reading. The 12.3 also matches the reading my inverter shows, which is about 14 if I'm running the truck itself.