Sooner or later, you are going to need to pull a wire or two through the boat. This is not always easy, especailly if you are feeding the wire through a tubular radar arch, wakeboard tower, and so on. But there are a few techniques we can borrow from the communications industry that will make this a whole lot easier.
There are a few essential tools that need discussing. First is the "fish tape". I am not making this up, its an "official" name. A fish tape is a length of steel, fiberglass, or other material that allows you to "fish" the wires through an area. In the electrical industry, fish tapes are used to pull conduit, and almost any well-stocked hardware store will have several to chose from. Look in the electrical section of Lowes, Home Depot, and Menards and you will find them.
Unfortunately, most fish tapes are just too large for use on a boat. But try to find one 25ft at the most, and with the smallest width steel tape as possible, such as this Klien Tools model 56005, Ideal 7529, or Gardner-Bender EFT-321P.
Even with the smallest fish tape you can find, you will soon find its also too large for certain jobs. I use and highly recommend two more fishing devices shown here. On the left is a 50ft coil of 1/8" nylon tube with hooks on the end for pulling wires. Fifty feet is more than you need, and it can sometimes get tangled. But its a low cost item, and you can cut it in half if you wish. This tape is the one I always use when fishing wires through my Radar Arch, as it has the flexibility to go around sharp tube bends. If you are trying to install speakers in a wakeboard tower - use this. The item on the right are fiberglass rods that screw together to make a larger pull rod. It is useful in areas where you cannot easily get another type of fish tape to work, such as through bulkheads. As each rod is 11" in length, it is sometimes the best solution. Both of these are made in China by Cen-Tech, but don't let them fool you, they work surprisingly well. Amazon, Harbor Freight, and others usually carry these items.
You can buy other accessories for fishing wire and cable, such as this fish tape eyelet that grips cable ends. You can also buy pulling lubercant to help in yanking the wires. However, I find that these devices are usually too much for boat use, and in the case of the lubercant - makes a mess. So this stuff is usually best left on the store's shelf.
In a boating environment, you will find different cable and wire pull jobs; some cable ends with pigtails, as well as some pre-terminated cables. So I will provide a couple of examples of how I prepare the ends.
Regardless of which fish tape you use, there will be some sort of hook on it's end. When pulling a pigtail, simply bend the ends of the wire to make the connection to the fish tape.
Then simply tape the entire connection with electrical tape. Here you want to make sure there is not too large of a bulge so that the splice will fit through any bulkheads, as well as not too long, or the splice won't go around bends easily.
Quite often, you have to run pre-terminated cable; that is - a cable with a connector already on it. In many situations, you cannot easily remove the connector, so you will have to pull the entire cable with the connector attached to it. To wrap this kind of cable, start wrapping the cable with tape below the connector, then insert the fish tape's hook somewhere along the wrap. The idea here is that you do not want to pull on the connector itself, as you may damage it, or worse - pull it off.
Continue with the wrap until you have wrapped the connector as well. One word of caution; often the connector itself will present a flat end that can get hung-up in the wiring tray. To prevent this, try to form a "nose cone" out of the tape leader, or even use a piece of wood - fashion it into a cone, then tape it in front of the connector.
Another scenario is an end with multiple connectors. While the tendancy might be to just wrap all of the wires together, it will create a rather large ball at the end, which may be impossible to feed through. There is a better way.
Fold the connectors back onto the jacket, one by one, and stagger them so that a minimum cross section is created. This does take some time, but the result is a smaller cable.
As in the other examples, simply wrap the joint with electrical tape until everything is secure. And as before, try to form a nose cone of sorts if you can as this will make it easier to pull.
I'd like to share one last tip, borrowed from the telecommunications industry. As you are taking all of the trouble to pull a wire, especialy if the wire pull is in a cable-way where additional wires may be pulled (i.e. main cable way from the salon to fly-bridge), pull a nylon rope along with the cable. You can buy special rope for this function; called "pull rope", but any 1/16"dia or so general purpose nylon twine will work. When you finish with the pull, tie the pull rope off somewhere at the distant end. Then at the source end, pay out at least as much length as you pulled, then tie off the near end, then coil up the remainder. You now have a permanent pull string so if you need to add any wiring, you can simply tape the cable to the pull string, then pull the excess string through at the distant end.