Question about external GSP antenna on Garmin

[Brioche]

My boat has an old depth finder that reads out on the traditional dial over the companionway hatch that is hard to read at night. I installed a second transducer to read through the hull for attachment to my older Garmin because it is easier to see at night. It turned out that I needed to get a different power cord/wiring harness for the Garmin that had a socket to plug in the transducer. I discovered that the present harness instead has a socket that fits a plug that runs to an external GPS antenna in a puck on the rail. In other words, I have two harnesses, one that plugs into the antenna and the other that plugs into the transducer, and in both cases there are also some extra color-coded wires left hanging loose. I would be able to either hard wire those or attach them to my own connecting plugs. Garmin support was not entirely helpful. My questions are these:

1) The GPS seems to work fine with the external antenna disconnected -- is there any advantage to keeping it?
2) Am I right in assuming that I could use the loose wires on either harness to connect the device that doesn't have a matching plug, that is, either the external antenna or the transducer?
3) Is it likely that the color coding on the Garmin harness is matched by the color coding on either the antenna or the transducer?
Thanks