After going through all of the cost and trouble to put a good quality heat shrink and adhesive lined electrical connector on, the last, and maybe the most important step, heating the jacket to seal it up, is skipped. This is something that we see regularly while crawling around boats. One might suspect that it is only the DIY crowd that would miss such a critical element; however, these pictures are from a factory installation. And there were several.
The advantage of heat shrinkable connectors in the marine environment is the watertight insulating layer around the conductor mechanical interface to the connector. This prevents exposure to moisture. It also mechanically relieves strain from the conducting wire to connector interface. Foregoing shrinking leaves your electrical connections weak and open to the elements, leading to corrosion.
Faulty connections may cause electronic malfunctions and other easily avoidable electrical problems. Save yourself the headache by using or borrowing a friend's heat gun to complete the connection. If a heat gun is not available, a blow drier on it's hottest setting may suffice. As always, use caution when applying any heat source.