7 PIN Plug Wiring

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7 PIN Plug Wiring

Postby tx63conv » Wed May 17, 2017 6:34 pm

I recently bought a new 20' cargo trailer. They checked the brake lights and turn signals before I left the lot and everything appeared to be ok. I didn't physically check the lights.

Recently I scraped the bottom of the trailer at the rear corner and the wiring harness that runs through the ramp door to the tail lights was cut in half. I have a wiring diagram and spent a some time connecting everything back together. Everything works except my brake and turn signal on the left side. Based on the wiring diagram this is the red wire.

I checked the red wire were it was cut in the wiring harness coming from the truck with my multi meter while the hazards were on. Nothing...no voltage. I checked the wire further up just past the 7 pin plug and still nothing...no voltage. I checked the brown wire which runs the right side brake/turn signal at the same spot grounded to the same white ground wire and I got flashing 12v.

My question to the group is where to go next? My thought was to run a 12v battery directly to the red wire just past the plug and see if I get brake lights...that will at least tell me the wire from the plug to the brake light does not have any issues. This will narrow it down to the truck side of the plug or the actual trailer plug.

Any other thoughts? I don't want to haul it back to the dealer.
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Re: 7 PIN Plug Wiring

Postby Dale M. » Thu May 18, 2017 9:09 am

Not knowing what your tow vehicle is, but my 2005 Chevy PU has separate set of fuses for tow lights on trailer... Might check owners manual and fuse box... Also you did not say of stop/turn signal is functional on TV...

Might try using a test probe in socket on TV side of system, problem may not be in trailer at all... I have all sorts of exotic meters and tools and I find this best tool ever...

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Re: 7 PIN Plug Wiring

Postby les45 » Thu May 18, 2017 11:44 am

+1 on checking the fuse box first. My neighbor had a similar problem with his RV and the RV guys told him he needed a new converter. After spending a lot of money on it and still no fix, he took it to a local shade tree mechanic who changed a blown fuse and that fixed the problem.
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Re: 7 PIN Plug Wiring

Postby tx63conv » Thu May 18, 2017 5:23 pm

Exactly what I was looking for. Turn signals brakes do work in the tow vehicle but maybe a blown fuse for the plug? 2012 GMC Sierra. I will investigate
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Re: 7 PIN Plug Wiring

Postby tx63conv » Fri May 19, 2017 3:00 pm

Exactly what it was....thanks guys!
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Re: 7 PIN Plug Wiring

Postby Shadow Catcher » Fri May 19, 2017 6:37 pm

Basically you start with where you have power and follow it to where you do not, the problem is some place in between. I do have a tester to check the plug at the vehicle. I have found problems with grounds, one side marker light was wire in backwards, LEDS do not work, the seven prong plug has had a problem with corrosion...
Do let us know what you find.
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