OK, quite a few post asking about 4 wires going to a 24V system. First, a little background. In the late 80's/early 90's we didn't have on board chargers. The first onboard charger I remember seeing was in a Basscat somewhere around 92/93. To make charging easier, the 4 prong/4 wire system became standard on several bassboats. This, in effect, moved the 4 battery post up to the boat side of the plug and configured them in such a way as the two negatives were side by side and the two positives were side by side. Putting a jumper in the plug allowed for the 24V jump and gave 24V when wired to the proper terminals, 12V when wired to the proper terminals, so you could achieve 12/24 also with a three wire trolling motor connection. Each positive wire going to the front had it's own breaker. This system allowed for a separate plug to be purchased (usually red) and it was wired internally to two jumpers, one connecting the positives and one connecting the negatives. This plug was wired to the portable battery charger and when ready to charge, you simply plugged the charger into the trolling motor plug. When 36V systems became common, along with onboard battery chargers, this system soon became obsolete.
So we have several boats still with this system. For those dealing with it, there is two options. Keep as it (if it's working, don't fix it) and when you change batteries, simply make sure you connect each "pair" to a battery. A breaker of the correct size still needs to be in each positive wire going to the plug. Second option is to reconfigure. This must be done carefully since if you connect the wrong pair to the batteries and place the jumper, it could create a dead short when plugged in. To go to a two wire system, you must trace the wires to see what you have. The easiest way to trace them is to remove one pair from one battery, then on the front, identify the pair that has 12V on them and mark them. Remove the other two wires from the front and let that pair just lay in the boat. Now, at the back, take the positive off the positive of bat 1 and move it to the positive of battery two. At the front, place the negative on the terminal that reads bat 1 negative. On Rangers, this is not marked but it goes to the top left (looking at the front of the receptacle, alignment notch at the top) and the positive goes to the bottom left, or to battery 2 positive. At the batteries , place a jumper from the positive of battery 1 to the negative of battery 2. If you have a 36V motor, battery 2 will become battery 3, you'll add battery 2 and place jumpers from battery 1 to 2 and from 2 to 3 in the same manner as above. The front will not change.
A breaker of correct size will go on the positive wire going to the front. This is the only breaker needed.
Hope this helps
John