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This Old Trailer: Troubleshooting the Ground Wire

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Written by:
Lindsey S

Edited By:
Leah B

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Troubleshooting the Ground Wire Episode of This Old Trailer


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 Video

I installed new trailer wires on my ice fishing house. The turn signals, brakes, 4 ways work great, but when I turn on the lights, everthing shuts down.... nothing works.This trailer has a down tonuge that is hinged so it can remain connected to the trailer hitch.Do I need to ground the lights them selves by running a wire from the mounting bolts to the frame or...?I tested the lights on the truck and seem fine.

comment by: Gary C - 1/13/2013

823

I would start by checking grounds. It sounds like you have an insufficient ground. It is enough to run the signals individually, but when you fire up the running lights, there is not a good enough ground. Check the ground wire at the trailer connector. Make sure each light is properly grounded. Some are stud grounded on the mounting hardware, others have ground wires. If your trailer frame is aluminum, it may not be providing enough ground. In which case, you can add ground wires to the lights and bring them to one common ground that you can run up to the trailer connector.

Patrick B - 1/22/2013
509

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thanks. this is exactly the information I needed about testing ground.

comment by: Brian - 1/22/2013

885

You are welcome. Glad to hear we helped.

Patrick B - 2/1/2013
553

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