GETTING MY SOLAR PV HARNESS SUPPLIER TO WORK

With all the increasing variety of apps for PV technologies, there was a need for a safe and simple-to-use solar panel connector, This is often when MC3 solar connectors were being made. it is a dumb dilemma but I’m not solar panel savvy. What do the rubber plugs at the end of solar panels do? Are they vital? I've 3 that are missing and I used