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Blowing 7.5 Amp Fuse When Turn Signal Used on Tow Vehicle

Question:

I had the Honda dealer install a towing wiring harness about 5 years ago. It was either a Honda OEM part or third party Curt or Tekonsha so there was no splicing etc. Now I cant keep a 7.5 fuse in without it blowing. the dealer put all the wires in corrugated loom so none are in the elements. I realize there must be a short somewhere, but I dont see where there are any wires touching metal? You provided the additional information, "1. Yes, it's 4-pole connector. 2. I've attached one of the photos and renamed it Photo 1. The 7.5 amp fuse only controls the trailer lights. The fuse is part of the wiring harness that the Honda dealer installed. When I pulled the interior trim off I noticed the fuse, replaced it and the lights lit up on the tester, but when I turn on one of the directional lights I went back to check the tester, nothing. I looked at the fuse and it had blown. 3. I don't lose any blinkers on the vehicle, they all work. 4. No, it only blows the fuse after I turn on one of the directional lights. Actually my neighbor came over with his car, we hooked up the trailer to his car and all the trailer lights worked, no fuse blew on his car."

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Expert Reply:

Through your testing you have proven that the issue is on the vehicle side and not the trailer side. Your four pole connector has a wires colored green for right turn signal and brake lights, yellow for left turn signal and brake, white is ground, and brown is marker lights.

I have included a link to a trailer wiring FAQ that you may wish to review.

Like you, I suspect that you have a short, and probably on the green or yellow wire. I would use a electrical multimeter, set it for “continuity.” Put one probe on an exposed metal spot for grounding then test if you have continuity to either the green wire or yellow wire. This will tell you which wire is shorted. Once you identify this, trace that wire looking for any cut or frayed portion that could cause the short. If you don't have a meter you can purchase the # PT89ZR Seven-Function Multimeter.

If all else fails you can pull out the old wiring entirely and replace with Tekonsha # 118438 Wiring Harness. I have included a link to an installation video on a 2008 Odyssey.

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