trailer wiring diagram. issues

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Original poster
Dec 4, 2012
Slower Lower Delaware
I am not sure if I stuck this in the right section. It is the beginning stages of a smoker build but for now I just need to get the trailer lights put on so I can transport it.

I bought a 7 blade wiring harness and a plastic junction box/wiring terminal online. I was going to go with just a flat 4 pin but decided just to stick with a 7 blade for the future. I have been online researching and have found tons of different wiring diagrams for a 7 blade harness. Which one do I go with?

He are all the details that I have, if they matter.

- Trailer will be towed with a 2003 Chevy Tahoe (the truck has a Hopkins aftermarket wiring harness with a 4 pin and 7 blade connector)

- Trailer will NOT have brakes (future)

- Trailer will obviously have brake lights, side markers, tail lights, left/right turn signals, license plate light (since trailer is less then 80" wide I wont need rear markers)

My rear brake/stop/turn lights are one 6" LED light

Side marker lights are 2" amber LED lights

License plate light will be a standard LED license plate light

- The wiring harness I bought says "SAE J1128"

- Here are the wire colors and sizes for the harness

* White / 10 gauge
* Black / 10 gauge
* Blue / 12 gauge
* Green / 14 gauge
* Red / 14 gauge
* Brown / 14 gauge
* Yellow / 14 gauge

How do I know what diagram I need to go with. There are so many I don't even know which ones to even post.
I just was thinking, on a standard 4 pin harness, its wired just the same right? just 3 more wires, red, blue, and black... right. so wouldn't it be

Brown - side markers, tail lights and license plate

yellow - left turn signal

green - right turn signal

white - ground

then what are the red, black

I assume blue is aux/brakes??
Also, I took the harness out to truck, plugged it in. I took one of my lights and connected the white to the white (ground). Then went thru the rest of the colors. Here is what I found controls what.

Blue - Nothing

Yellow - Nothing

Black - Nothing

White - Ground

Brown - Right Turn Signal & Brake Lights

Red - Left Turn Signal & Brake Lights

Green - Tail Lights

Also, When the turn signals are ON and brakes are applied, the Turn SIGNAL is active.

I am completely confused.

Yes I know I can always wire it up and just connect the appropriate light to the corresponding harness wire, but I want to do this right. I don't like half assing things.
The red is to charge batteries on a camper. Black should be a ground wire.
Here is another one. The colors used to be standardized, but with the advent of inexpensive Chinese imports they may not all be the same any more.  I know one I bought off eBay was color coded different and I ended up plugging the trailer pigtail into the truck and verifying all the wires with a volt meter.

I wired all my trailers to the 7 bladed plugs, even the ones which came with 4 terminal plugs like the utility trailer & boat trailers.  Since the truck had a 7 blade from when we owned a travel trailer, it just made it simpler to not have to worry about an adapter that might wiggle out or get lost.  Just remember it matters how you are looking at the plug or the outlet, otherwise it's easy to have wires reversed.

Also that Tahoe should have a factory installed fuse position for the auxiliary charging line.  It needs to be on a 10 gauge wire and is one of the big maxi fuses in the under hood fuse box.  Not all aftermarket installations use the charge line so if you have no voltage there, it may not have been hooked up previously.  Again a voltmeter would be your friend in diagnosing this.

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Also, take a test light and make sure your truck is wired right. especially if it's an aftermarket plug.

We have a company with many trucks and trailers, and someone is always ripping out a plug, then not wiring it back correctly, or just getting what they need to work to get in..

If you wire to those diagrams shown, your trailer will hook up to probably 90% of the vehicles out there as that pattern is fairly standard. Your yukon will  also hook up to most of the trailers out there. Don't loose a lot of sleep over the colours and worry about the positions and the positions shown are quite standard.

Ok, I feel light an idiot. I just checked the page I bought the harness from. There was/is a diagram on there. But I guess for future reference, here is a diagram if anyone else ever had is issue.

#4 in this diagram is not so much for charging batteries on a camper as it is hot all the time (it will charge batteries tho as well)...even when lights and ignition are off.... I use it for a cargo light in/on the trailer so that you don't need the running lights on to use the cargo light (just remember it can run the battery down enough that the truck won't start)
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