Hesper, if you don't have the installation manual it should be available online. Find out how it is SUPPOSED to be wired up, then make your wiring be the same way.
At a certain point it will call for plus-and-minus power connections and quite possibly a ground as well. If there's no common ground bus in your boat, this is a good excuse to run one, at least as far as the autopilot and instruments.
A spool end of tinned 'ground braid' or tinned large-conductor wire (or "machine cable" which is similar to battery cable) can often be found as surplus on ebay for reasonable prices, so you can be generous with where and how you run it.