7 pin trailer plug, wiring reverse lights on trailer

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Jul 17, 2018
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LUGOFF, SC
I'm thinking the best way to do this would be to tap into the reverse light circuit at the rear of the truck and run that signal through the 7 Pin plug to trigger a solenoid on the trailer and use the trailer's battery to power the reverse lights. Doing this would also allow me to switch the power on the reverse lights to become work lights without back feeding the truck.
Anybody do this?
 

ppc

M Go Blue
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Aug 18, 2003
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Nashville, TN
In addition to incorporating a relay in the trailer's electrical system to control the trailer I would also use a relay in the LC/LX reverse light circuit to supply a true 12V to the 7-pin plug.

My experience indicates that the wiring that supplies the vehicle backup lights is undersized. Several years ago I discovered that using higher wattage bulbs caused a significant voltage drop. I pulled one of the two bulbs and the brightness very significantly increased so I ran a 14 gauge test wire directly from the battery to the bulbs. Both bulbs were brighter than the single bulb using the factory wiring. Even the normal wattage bulbs produced brighter lights during this test. My boat trailer used an electric solenoid to disable the surge brakes when reversing. The solenoid operation was marginal because of the voltage drop was even larger.

With a 7-pin setup you should already have a good 12V supply at the connector that you can use to power the external backup light circuit through a relay. This is a good solution in that any trailer you decide to tow will be fully capable electrically not just your own trailer.
 
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Mine came with the remains of something that let the magic smoke out a decade or more before I got it and a mangled twisted bracket under the bumper that might have held a 4 prong plug at one time.

I put in a new 4 prong system because that's all I needed. Now I need a 7 Pin beast to fit my new adventure trailer.

PPC, there currently isn't a dedicated 12V line running to the 7 Pin plug. The trailer is rigged for it to charge its onboard battery when traveling, but I haven't run the line yet. I'll run it when I run the brake controller wire. That's a good idea to run a "real" wire for the back up lights, "just in case". I was being cheap with using the signal from the back up lights to run the full power system dedicated to the trailer. I'll find a 10/3 stranded bundle and run that down through the rig.
Now I need to find a good spot to hide a relay on the reverse light circuit. Probably behind the jack in the DS rear corner, there should be room to tuck a little bracket in there some place.

I tucked the 7 pin up in an armored cubby. If I peel it off I've done something really special.
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60wag

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Jun 25, 2003
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Boulder, CO
Most of the newer trailers are running LED lights which draw much lower current than the old incandescent trailer bulbs. The hoops I jumped through to get my old 60 to light up old bulbs sucked, had to switch to a controller with a battery feed. My new trailer is all LED and the lights work well with a splitter tied into the rear light harness. Wiring the rest of the brake controller with some decent gauge wire was a bit more challenging.
 

Dissent

Questioning my life choices...
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Sep 27, 2012
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Loudon, TN
I ran a relay on my backup lights since I had an extra in my relay bank. Made it easy to go from the bulbs to the LED spots on my license plate...I do have a spare 42" lightbar in the shed...;)
 

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