If it showed that while cranking, I'd say it is OK, but if that is just "key-on" it's not good. Have you checked the voltage at the B+ terminal of switch with key on?
Next test. Connect voltmeter positive lead to the B+ terminal of switch and the negative to the "Ign" terminal. Turn key on and read meter. tell me what you get.
If the boat starts and runs, what is the voltage AT THE BATTERY?
What sort of rewiring did you do?