Re: i need help again please....
Finding a short is not always easy to do.
You will need a multi-meter set for measuring resistance. If it has the audible feature that makes a chime when continuity is detected, that can really make things faster.
I would disconnect all wires from the (+) terminal of the battery. Leave the (-) wires connected. Hook up your multimeter to one of the ground wires, or better yet, directly to the (-) terminal of the battery (ensures you have good ground reference). It would be a good idea to disconnect the ECM. Taking a resistance of computer circuits is not a good idea.
Then, go to the wires you disconnected from the (+) terminal and check each one for continuity to ground. You stated there were a couple you did not know where they went. Well, if you get a low resistance reading (or the beep in continuity mode), then that wire is the one that is shorted. Still check the others, just to make sure you do not have more than one.
To isolate it further really depends on how your boat is wired and what stuff you have. Basically, you will need to follow the wire that showed indications of a ground and visually inspect it until you run out of wire. If you come to a component of some sort, try to unplug that component to eliminate it. For instance, you are following a wire and it goes to the radio, pull the main plug on the radio and check that wire. If the ground goes away, then it is something in the radio or it's in the plug. If the wire is still grounded, then you missed the problem and you need to start heading back towards the battery.
It will get really complicated if you have a terminal board or some other type of junction that then feeds many different circuits. Your fuse panel is one such location. However, from that main junction, each circuit downstream should have it's own fuse. Pull the fuses one at a time, until the ground goes away.
Big picture, most parts of a boat are not GROUND. Meaning, they do not conduct electricity and are not electrically common with the (-) terminal of the battery. (Unlike a car or truck, where the whole thing is metal and the (-) terminal is tied to the chasis.) This is why you must run two wires to almost everything in the boat. One to supply the (+) and the next to return it back to the battery (-).
The biggest area where a wire could get "grounded" to something metal is the engine. Take a close look at the wiring harnesses around the engine bay. See if any are pinched, chaffed, etc. Another thing I would look for is any wire that is getting "pinched" in any hatches or other places that might see some sort of movement.
Now, the fact that you have a short and did not blow a fuse is reason for concern. The purpose of a fuse or circuit breaker is to protect the wiring from excessive current (leads to a fire) which normally results from a short. There should be VERY LITTLE runs of wire with no fuse or breaker protection on the boat. For instance, the wire running to the main breaker (on my boat it's at the rear of the engine) is unprotected from shorts UNTIL the breaker. So, if that run of wire were to get grounded to the engine block, then I would have an unprotected ground. If someone has directly wired a bilge pump, radio, or ... to the battery without a fuse or breaker in the (+) leg, preferably as close to the battery as possible, then they have screwed you.
Only other thing I can think of, would be a wire that is submerged. A solid wire should be ok underwater, but if it has splices, connections, or some type of plug, the water might be creating the short. All the connections on the boat should be protected from water. A spice in the bilge, is just a bad idea.
I hope this helps some. There are companies that sell boat wiring harnesses to. If your harness is too full of "issues", it might be easier to buy one of the harnesses and wire it up fresh.
