How To Prepare your Trailer’s Wiring Harness before you install it

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    If you are thinking about building a Kit Trailer you will find out that there are a number of things you really should do before you put it on the road.

    One of the more important parts of your trailer is its wiring harness. The basic harness will come with a light kit and a blade connector to attach to your car or truck’s trailer connector.

    Although most of the parts you need are included the harness its self should be prepared before you install it or you could end up with wires that get damaged during use.

    This is very important if you are building a folding trailer but for any trailer of any size or design it is important to review how it will be attached to your frame and the potential failure points you must account for.

    Anywhere the harness is attached with a metal clip or passes through a hole in the frame you need to protect it from rubbing.

    Clips are sharp and will cut through the shielding on the wires even with slight movement or pulling.

    The folding pass through holes on the frame are also a major concern because every time you fold up the trailer for storage those wires will get jammed and tugged on and when they are tugged on they will pull against the clips.

    The part that will see the most abuse is the blade end and tail that runs from the trailer to the vehicle.

    Most kits will provide an harness that is normal shielded cable but if you want the harness to last you should protect it.



    To protect the tail end you will need 10mm heat shrink tubing for the main wires and 1/4 inch heat shrink for the ground wire. Measure out the appropriate length and place it on the cable first then shrink it in place.

    You can then use zip ties to attach it to the frame in a way that it won’t be damaged while in use or storage. You have to get a bit creative when attaching it because normally there is no provision for securing it.

    Additionally for the ground cable I suggest that you use liquid electrical tape which is like a rubber material you can brush on to coat the last few inches of the ground wire. This will give you good protection.

    For the rest of the cable since it is 2 wire cable you will want to use 1/4 inch heat shrink tubing over the entire wire harness however you may need access to the wiring harness at a point on the side of the trailer to make your connection at the side marker lights. Simply put two shorter about 5 foot lengths of heat shrink tube on the first section after you have figured out where you need an open area for the side markers.

    Then continue down the rest of the harness on both sides with 1/4 inch heat shrink tubing.

    Rubber grommets for the frame pass through holes would be a great idea if you can get some but you can also just double up on your heat shrink tube by using a larger size in that area or maybe you can use a piece of rubber vacuum tube used in most vehicle engines.

    When the harness exits the interior frame and passes to the tail lights you want to make sure that you route it against the bracket and not let it hang free.

    Heat shrink tubing can be heated to form corners and if held in place while cooling will take on the shape of the bend pretty well.

    You can then use zip ties to secure it to the bracket.

    All of this work will take you much longer than the normal throw it together instructions provided with your kit. However if you do not take the time to do this now you will be purchasing a new harness or repairing yours in a very short time.

    Final Note

    I really wish I had taken my own advice here prior to building my first kit trailer. Instead I pieced together and heat shrunk only portions of the cable harness in the areas that would see the most abuse.

    Just do this.. its only $10 worth of materials and it will make your life so much easier.

    I strongly suggest that you purchase about 25 feet of 1/4 inch heat shrink and 15 feet of a larger 10mm tubing before you start. Just shrink the whole harness except the parts where you need to make connections.

    You will also need a heat gun to shrink all of this heat shrink tubing you can’t use a lighter or a torch. You should also use it on its cooler or low setting as heat shrinking lots of wire can also heat the wires inside the tubing. Take your time doing it.

    Another option is corrugated harness protector. Unfortunately the sizes commonly available are too large to fit through the 3/8th inch holes in your frame. It is an option though.

    What ever you do you should really commit to doing your wiring correctly and at the very minimum I would suggest wrapping any wire area that will receive a metal clip …. with electrical tape. This will provide some protection from the clip cutting through the wire.

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