New to forum, just started to do my own work since warranty ran out. I am only reading 10 amps. Just replaced original batteries and seemed to be getting a some charge. This is my first diesel, so I am a little hesitant. Is this just an alternater going bad? Any help would be great, thanks.

Check all 3 cbles for green corrosion where the wire enters the terminal

Check the connections where they tie to the block and starter.

Check the body grounds, and the main grounds at the passenger-side rear of the engine

Pull the plug from the alternator, then plug it back in

If none of that corrects the low output, autozone and others can test the output if you take the alternator in.