Boat light wiring help

[CP]

The fuse is to protect the wiring in case of a fault.  The fuse rating needs to be high enough to carry the normal current without blowing but low enough to blow before the wire melts.  Anything from 5amps to 20amps (ish) should be fine.  I'd go lower than 20, maybe twice the current rating of all the loads added up.

[Pete112288]

Thanks everyone for the help. I have a fuse holder set up and 10amp, 15amp and 20amp fuses on hand, so I will look up the specs of the lights and sonar and go from there.

[Pete112288]

So after rewiring everything up, it all is working besides the sonar, I haven't checked its cable since the first issue so I think it may have damaged wire. But all the lights work correctly. As does the starting of the motor. Still have not wired them up at the same time yet. But I took my multimeter to it today to make sure of a few things.
It is reading that the metal of the trailer itself has about .20 volts give or take. There is no source of electricity no battery, not even a flashlight in the boat, took the battery out. Nothing is hooked up. But it reads that the trailer has a tiny charge and when I touch the positive of the multimeter to the shaft of the motor and the ground to the boat hull it reads .06v. Could all these small readings be static in the air or something? Might just be overly paranoid but I just don't want another issue.

[MIKEXRAY]

If there's no source of power whatsoever then my guess is that it is just ur Multimeter itself giving you those low readings, I wouldn't use those measurements to give u any concerns. 

[Pete112288]

So this thread is turning into a lot more than I expected.
Everything is rewired, with fuse added, and it works fine when hooked up at the same time as the motor electric start.
But when I flip the switch for my bow nav lights, it blows the fuse, any size from 5 amp to 15 amp, it blows. They are just 2 small 3 inch led strip lights in the bow.
If I hardwire the lights with no switch at all, or a traditional switch it goes fine. Nothing blows, and the lights come on fine.
I use the marine switch with 3 prongs and wired per the diagram, and it blows. I will put a pic of the switch diagram.
Can't find a round switch that fits my console that only has 2 prongs. I am so confused as to what it could be.

[Ridgeratt]

If the switch is not back lit you really don't need to ground the switch.
Try unhooking the switch