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How To Troubleshoot a Modulite Demo

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Demo on How To Troubleshoot a Modulite

Today we are going to troubleshoot a modulite that is not really working so we will check it out and show you what to look for. This will apply to all modulites and this will also apply to converter boxes as well. The only difference being that it does not have a power wire for a converter box. The first thing we want to do is put a tester on the 4-pole just to make sure. We will hook up our ground to our ground lead and then we will turn on the left turn signal which we have going, we have got nothing. You can turn on the other signals and see what we have got, nothing here. Try the running light circuit, nothing here either. 00:28

We checked it at the 4-pole with the tester right here, it could be something simple as a bad ground where it is connected up to the body of the vehicle. To double check yourself take the ground clamp and ground it to some where else to the vehicle. It is best if you can find it if there is a ground screw in the body itself. That will be the best place to do it. Then we will double check our 4-pole one more time, just to make sure it was not the ground. We have got our left turn going and nothing. So it is probably something further up stream. At this point we want to check the input going into the module. We will check our yellow wire that is the left turn signal and we will verify input going into the module. That proves that we have got input going in. Lets check the other inputs as well. 01:07

We are going to check running lights and the right turn signal and the brake signal. We went through all of those, we have got input, now the last thing we need to check for is our power supply for the module. Lets check that. We are going to check in front of the connection just to make sure that this part has not gone bad. That might be part of the problem right here. There is no power. With no power going to the module that means the module can not work at all. Lets go up to the battery and check our fuse holder and check the fuse. Take the ground clamp and ground it to the battery and we will shut the fuse holder. You do not have to take it out, we will just check it electrically because this little tab is on top. You have got power here, lets check the other side of the fuse, nothing. So the fuse is bad. So at this point replace the fuse and then we will check our module one more time. Lets check the 4-pole one more time and lets try the left turn signals. We have it blinking and that is not right because we have got a constant signal. It should be blinking with the left turn signal. That will tell us that the module is damaged and we are just going to have to replace it at this point. There you have it for trouble shooting a modulite and again this will work on this modulite and also regular converter boxes as well.

Dave R.


I hardwired the harness kit that the ford dealer gave me on my 2016 ford escape. The harness didnt come with plug in connectors. I get turn signals left and right, running lights but no brake light.

Etrailer Expert

Rachael H.


If the tail lights and turn signals are working is could be either the brake signal connection, or a bad ground. I would check the vehicle hardwire connection and make sure this it secure. Since activating the brakes typically puts the most load on the wiring if the ground is bad this is when it is most evident. You would want to check all the grounds on the wiring harness, at the trailer connector, and all the grounding location on the trailer (each light too). I have provided a link to one of our help articles that would provide additional details.

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