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Trailer Wiring and Light Replacement Demonstration

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Demonstration of a Trailer Wiring and Light Replacement

Today were going to be replacing the wiring on this trailer. We will be replacing a 4 pole flat, as you can tell this one is pretty beat up and worn, so it has to be replaced. We are going to cut this wire off and we are going to replace this brown wire also. We are going to cut this loose and pull the rest of our wire through, on this trailer here it is pretty open so we can reach the wiring. Just in case though, if your wiring was run in conduit and you are replacing it, do not pull all of this out yet. We will actually tie on the new wires and use these wires to pull them through. We are going to cut off all of this old wire here, and we are going to take off this old light too. I would like to point something out on this 4 pole flat, you will notice there are actually 5 wires coming out of it. What is happening is on the inside of this pin, which is for the running lights, has two wires coming out.

The reason for that is we can split the running light circuit to both sides of the trailer. Mainly that is used on boat trailers and other light duty ones. What is nice about that if you have a running light on the side, chances are your running wire right next to it. You can tap into your wiring without having to make a wire go all the way across. It basically provides a short cut. This case we are going to run it all the way on one side and jump over since we have a small trailer and no running lights. Now we are going to tape our new wires to the old ones and pull it through the frame. It does not take much, just enough to make it smooth so it does not snag anywhere. Now we simply pull the wire through. Before we pull everything through, we are going to make sure we have enough leader to hang out. This unit comes with a pre-wired ground wire so we are going to leave it at its maximum length and this is where we are going to ground it at and well have a good idea of how much slack we need to leave. At this point its a good idea to tape up all the wires together that way it will keep them from getting tangled with anything else. Since we have our ground here we are going to ground it but before that we are going to take this loop off for a smaller one. Since we have an existing ground that works pretty good, we will use a smaller screw. Always give it a twist when you crimp it down it will make a nice tight fit. We will re-install our screw but first we will put a pit of dielectric grease on there to help protect it a little bit, electricity still flows on the ground and the less rust the better. Now we can pull the rest of our slack out.

We have our lights pulled over to the left hand side, we are using the yellow and the brown, yellow for left turn. We need to cut this wire to length about 1/2 to 3/8 inch. The wires then get stuck inside here there is a little strip in here that pulls against it and when you pull it back it catches so it can not come out and makes electrical contact. You bottom out the plastic and give it a little bit of a pull back and it catches. Same thing with the left turn signal. If you notice there is two holes side by side here. You could actually jump another wire from this hole here to another light, so it acts like a miniature junction box. This little channel here hides the wire so when you push it up against your frame it wont get mashed. Your light gets installed just like that. Before we bolt on our light we are going to clean this area out where the holes are that way it makes a good metal to metal contact with no rust and corrosion. You can use a file or scrape it if you are in a hurry but if you can use something more abrasive. You do not have to get these super tight, just snug them down and they will be fine. Again were going to use the old wire to pull the new wire through. Now were back on the right side of the trailer and we will do the same thing, we will run the wires and install a new light. Now we will install our wiring, green for the right turn and brown for the running light. One more final touch will be to run some loom clamps to the wire to keep it up closest to the bed. It does not touch anything, but it is better to keep it out of the way. At this point we will reassemble our trailer and test out the lighting. We have our trailer wired up, lets give it a test run. Notice we did not connect our truck to the trailer so we can make sure our ground wire is working. It is not a good idea to ground through the ball because it can be intermittent from bouncing around going down the road. First we will test the running lights then the turn signals, then the brake lights. We will do this for both sides. There you have it for our install of our trailer wiring harness. We used part number A35W42B and the tail lights we used, the left hand side was part number 432400 and the right hand side was 432200.

Info for these parts were:

Video Edited:
Zack K

Video Edited:
Joshua S

Test Fit:
Nicholas E

Video Edited:
Andrew L

Video Edited:
Mike H

Video Edited:
Dustin K

Test Fit:
Shane T

Video Edited:
Sue W

Video Edited:
Chris R

Video Edited:
Jacob T

Video by:
Kathleen M

Installed by:
Cole B

Installed by:
Randy B

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This Old Trailer: Wiring Trailer Tail Lights

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This Old Trailer: Finding and Fixing a Broken Wire Part 2

Next we are going to go to less obvious stuff. Say for instance you have got your ground wire hooked back up to the frame and weird stuff happening out back. We will have to dig into the wire itself a little bit. In this case basically you want to check your wiring connection. You have a wiring connection right here that could be a potential problem right there. Chances are whatever fitting you used to put the wiring together might come loose. And also we have something kind of obvious too. The wire here has a little bit of road rash on it. You can see the bare wires on the inside. Even though it may still be making contact eventually this wire here will corrode up inside there and it will just lose contact so we are basically going to have a broken wire eventually. Lets go ahead and take this apart here we will see what we have got on the inside. 01:14

This Old Trailer: Troubleshooting the Full Ground Wire

We have demonstrated all of these fixes checking the ground on the trailer. The trailer itself is actually used as a ground obviously. Now there is some cases where you boat trailer guys and some small utility trailers out there, the ground is actually carried in a separate wire that lowers the trailer frame completely. The same tricks apply to check and make sure your light is working. Again the connection to the light could be bad or it could be actually a smashed wire underneath the frame of the trailer or also up front where you have got a little bit of road rash dragging the ground. We will go ahead and show you next an example of that type of wiring on a different trailer. 01:04

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Now we will move on to another circuit. In this case it will be the right turn circuit. And we will just check the signal on that. On the right turn signal here again, the same principle applies. Start from the front and work you way back. What happens a lot is that on some of these lights here where the wire gets ran in behind it, there is a channel that these wires fit into. However a lot of times, even on brand new trailers. This wire actually does not fit in the channel, they miss when they put it together. The wire gets smashed between the light and the frame of the trailer. Eventually they wear down to a minuscule spec of wire that is visible but it will cause a short and all kinds of headaches.

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