I had low or no readings on one side intermittently, swapped the cables and worked out it was the generator. Removed it, ran it, worked fine. Cables all good, eventually after a lot of work, isolated it to the cannon plug on the genny. Looked clean and good but the 'spring' had gone out of the pins. Inserted three short strands of very thin copper wire into each socket before reassembly, problem solved. Not very professional, but it's lasted years like that.