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The first thing you want to do when you first start working on electrical problems is you want to divide and conquer. You have two parts here, the truck and the trailer. You want to verify which one actually has the problem. Chances are it is going to be on the trailer, but then again you still want to check the truck too. So use a separate light tester, hook a ground not to the frame but to the 4-pull ground itself because this is what is going to carry the ground to the trailer. :52
So we will hook up our ground lead to the tester to the ground, we have our running lights on so we are good to go. We will do the same test with the left turn and right turn. Once we verify our truck is working fine then we can start working on the trailer. The hitch should only be used for pulling purposes, not for anything electrical. And that is the proper way how the trailer should be hooked up to the tow vehicle. 1:19
Just to give you a quick idea how electricity flows in the trailer what happens is the electricity flows through the brown, yellow, and the green wire goes through the lights and has to flow back in a circle like I said, so it all has to come back to ground. On trailers it goes to the frame, and from the trailer it has to go through the ground on the truck. And if there is any interruption it is going to cause the trailer lights not to work at all or do some weird stuff. We have our ground wire right here, as you can see it is loose in the air so it is not going to do you any good. We have wires disconnected so lets go out back and show you what is going to happen when you have no ground wire attached to the trailer.1:54
You can see here we actually have the lights on on the trailer, yet we still have the ground disconnected up front. Basically what is happening is starting to get ground any way it can. In this instance it is getting it through the ball on the truck. Now you get a brand new hitch with everything painted and nice and new, chances are this is not going to work this way. But on an older vehicle, with the parts worn in and used a lot where you still have metal to metal contact it probably will work. However, it is not very good on an electrical system, because when you go down the road you are going to get a constant on off all the time. You have probably seen guys going down the road and see their lights flicker every time they hit a bump. We will shake the trailer and get the same effect. And now we have the turn signal on. Again, the ground is not hooked up front, but it is getting ground from the ball. We will go ahead and shake the trailer again. See how it goes off? That is not good. So to fix that we will go ahead and reattach our ground. 2:51
Go ahead and run the ground screw through the trailer. Now that we have it reattached go ahead and test it back at the other end of the trailer. All right we have the running light circuit back on, go ahead and check the trailer, simulate it bouncing down the road.
Questions and Comments about this Video823509
Today on This Old Trailer we are going to replace the wiring on this trailer. Right now, this trailer has a 5 pull socket here and the owner uses a patch cord in between here and his tow vehicle. What we are going to do is remove all this and add a 7-way cable that leads right to his tow vehicle. We will be using part number H20046. We will unbolt the connector here. Then we will go ahead and untape it and undo the screw right here, it should release the inside part where the pins are and the wires are connected. Tale that, push everything out. Simply disconnect our wires. 1:04
In this edition of “This Old Trailer” we are going to wire up the lights on this trailer. Previously we had hooked up electric brakes and you can see, right now we have the junction box installed on there and we have wires ran for electric brakes. We have nothing for the actual tail lights themselves. That is what we are going to start on today. :30
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
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
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.