These are something that has no place on a boat - wire nuts.
On Board with Mark Corke shows us the correct way for wire terminals. He says....
I recently surveyed a power cruiser which had lots of alterations to the electrical system, not only were many of the connections made with wire nuts the cable was solid core rather than multi strand tinned boat cable, both of which are a big no-no on a boat. Wire nuts are not moisture resistant and cable with a solid core is susceptible to vibration and fatigue eventually leading to failure.
For the complete step by step guide to making proper electrical connections continue reading ..
Wiring on a boat leads a hard life; corrosion, vibration and chafe all conspire against your boats electrical system to bring it to a premature end. Bad connections are to blame for many problems and knowing how to make proper crimped terminals will go a long way to avoiding problems. Simply twisting wire together, using wire nuts or wrapping it round a terminal screw simply will not do. Proper crimped terminals are neat, allow the free movement of electricity and prevent short circuits. It is a good idea to have some practice runs on some spare bits of cable so that you are able to make perfect joints every time. Tug on the connector to test the integrity of the completed joint; if there is any movement or the terminal comes off you need to cut back the cable and start afresh. Terminals and cables come in a variety of sizes measured by what is called gauge; the smaller the number the larger the cross sectional area of the cable conductor and therefore it’s ability to carry higher electrical loads. Always make sure that you use the correct size cable for the maximum amount of the current that the cable will have to handle. Finally only ever use tinned marine cable on a boat. Untinned cable is cheaper but is very susceptible to corrosion.
Tools and materials needed
Heat shrink the same color as the cable
Making proper terminal connections is very straight forward and easy but it pays to have a trial run with some scrap cable to get the feel for how things should go.
1. Cut back any suspect and ragged ends using a pair of side cutters or the cutters built into the crimping tool. This is especially important if the wire is at all corroded. You can skip this step if using fresh new cable from a drum.
2. Strip off the insulation from the wire being careful to cut only through the sheathing and not into the actual wire. Remove only sufficient insulation to allow the wire to be entered fully into the terminal with no bare wire visible.
3. Grasp the wire in one hand and with the other twist the strands together between thumb and forefinger. This binds the strands tightly together which makes pushing the cable end into the terminal easier.
4. Cut a length of heat shrink about an inch long the same color as the cable insulation and slip this onto the wire.
5. Slide on a terminal connector to the end of the cable and after ensuring that it is pushed fully home use the crimping pliers and squeeze it onto the wire. Note that the crimping jaws are color-coded. The colored dot on the plier jaws must correspond with the color of the terminal.
6. Slide the heat shrink back up the cable so that it covers the crimp completely then use a hot air gun or a match shrink it into place. Do not apply too much heat; warm it just sufficiently to shrink it to the cable.
7. The completed job. A perfect electrical connection, which should give years of trouble free service.