I have a MagneTek series 6300A model 6345 I had called Randy and he sent me a PD 4655. it is a 55 amp. looking at instructions and it says not to install a larger am unit than you are replacing. ...
The entire loop means (1) the main 12v+ from battery to the fuse panel (2) main ground/frame connection at the fuse panel (3) the ground/frame connection at the battery.
Electricity flows in a circle. If any section is under size it will reduce performance or overheat.