It's always best to chase down where wires go to before reconnecting, especially if you have any LED lights
as they won't work and can be burned out if connected in reverse.
As the PD-4045 doesn't have an internal grounding terminal strip I always set up an external terminal strip for all the grounds I need.. The Battery
(-) goes to a heavy stud, along with a cable to the chassis cround as well as the ground from the 4045 and one as a ffeder to the ground terminal strip.
If you are just installing, set up the AC first and get that working. You will have to install a master breaker and a separate breaker for the converter section and connect the wire for that before the converter will work.
will need at least a 20 amp fuse, the others should be good at 10 amps.
Don't guess, ask questions.