Troubleshooting a Blown Trailer wiring Harness on a 2012 Ford Edge EcoBoost

Question:

Before I purchase this part I needed a question answered regarding a malfunction in the converter I now have. The 3 green power indicator lights on the 4-way plug from my vehicle are on constantly and when I plug it into the trailer plug all running lights come on immediately even though the headlights on my vehicle are not turned on. However the turn signals and brake lights will not come on. All lights on the trailer work fine on another vehicle so I believe the problem is in the converter itself as this is my second one. The first one lasted 2 weeks and this one has worked fine since for an entire year until now so Im at a loss what to try next. U haul installed the wiring and says the problem must be a short on my trailer but how can a short damage the converter when the power comes directly from the battery on a fused line without the fuse blowing? Im not getting any satisfaction from U Haul so I just want to fix the problem myself. I suspect their parts are defective or they have wired it improperly somehow, not sure. But I need to know first if a short could possibly damage the converter when the power line is fused. Isnt that why its fused in order to prevent that from happening in the first place? I appreciate any help you can provide on my problem as I certainly dont want to put your part on to only have this happen yet again. Thanks,

asked by: Bob B

Expert Reply:

I hate to say it, but the company who installed your harness is probably right. We see what you are describing pretty often and the problem is almost always a short on the trailer. Or its that the lights on the trailer draw too much amperage for the converter and it shorts out like that.

The reason the box will short out and not the fuse is because the fuse is between the battery and the converter, whereas the short is on the other side of the converter box. The fuse protects the converter box from shorting out on the power side of the box, but if theres a short on the trailer side of the box it will take the box out.

I know its obnoxious that it does this, but it is actually designed to fail if the short on the trailer is too bad. Otherwise it would short out the tail light circuit of your vehicle and that could get expensive to fix.

I would thoroughly inspect the wiring of your trailer looking for shorts and fix them as necessary.

I attached an FAQ article on trailer wiring for you to check out also.

expert reply by: Jameson C