Heat-shrink crimp connectors have been used on boats for years to make reliable connections between wires. Most often, the connections are between two wires of similar gauge but when the wires differ substantially in size, the reliability of the connection can suffer. This can often be the case when connecting LED and modern electronics that draw low amperage loads to your boats factory wiring.
Your boats factory wiring for electronic accessories will range from 16-14 gauge however, your accessories wiring may be as small as 22 gauge. To ensure a reliable connection, use a "step down" heat shrink butt connector appropriate for the wire sizes you are connecting. Step down connectors such as the item featured below, will have different size openings on either end.