Here is another Volvo Penta KAMD 44 P-B video on the fuel pump actuator. This is part 1 of diagnosis of a the actuator and related engine wiring. Enjoy!
I had the same code on my KAD 300. At the same time I had a second code for a gearshift problem. I traced back the circuit just as you did and decided to replace the stop relay as both the actuator and the gearshift looked to be dependent on the same supply. Seems to have fixed the problem. These motors are getting old and there are so many connections that can be faulty. I’m going through all the connections cleaning them and putting the electrical grease on them plus I replaced all the relays.