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Old 10-07-2010, 11:39 AM   #1
KarenW's Avatar
Trailer: U-Haul CT
Posts: 62
simple wiring question

I do apologize if this has been covered. I did search both here and on the Uhaul forum, but I'm not sure I know enough to know if my question has been answered already.

I bought a Uhaul CT (best as I can determine it was the first year model (1984?) because the manual I downloaded from here talks about stuff added to later model and mine doesn't have them.

A previous owner had redone the wiring. He had a 4 pin connector to the tow, wired 6 wires (2 green, 2 yellow & 2 black) coming to the camper. I had either turning or break lights, but not both and charged the battery when towing. Once inside the camper there are several splits and crosses with wires that weren't the same color.

Since I purchased a new TOW with a 7pin connector, I thought to rewire the whole thing. I purchased a big 7 pin cable and have it going from the tongue to the camper. I've tracked most of the wiring to know what goes where, but with a couple of the splits, etc. I've downloaded several wiring diagram guides off the 'net and read the UHaul manuals posted here. I still can't tell a few of what I'd call "the basics".

1. Rear tail lights. I have the "amber" and "red" lights. Each has 2 wires (1 red 1 black) coming out with the standard connectors. Which should be the "hot wire" and is the other a ground?

2. I have the original battery box and converter. Does the aux line from my 7pin cable go to the battery (pos or neg) or to somewhere in the converter (if so, where in the panel)?

3. In the original wiring design where were ground wires attached to the camper?

Again, I do apologize if this is a repeat question or if I should have been able to find this information through a search. I'm just not a big fan of electrical and I am trying to overcome and learn

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Old 10-07-2010, 01:29 PM   #2
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Trailer: 1983 13 ft Scamp
Posts: 3,082
Try this site ,good info.Trailer Wiring Diagrams |
Click image for larger version

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Old 10-07-2010, 04:55 PM   #3
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Trailer: U-Haul CT
Posts: 62
Thanks. I actually took those pages printed to help me outside. I think I wired everything as indicated, but when I hooked it up to the tow, no go. I'm tired, frustrated and going to stop for the night... maybe it will go better tomorrow...
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Old 10-07-2010, 05:22 PM   #4
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Name: Greg
Trailer: Casita
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In your post, you mentioned amber and red tail lights...on the trailer, or on the tow vehicle?

My reason for asking, is that if these lights are found on the tow vehicle, but not on the trailer, you probably need to install a small converter box, which mounts under the rear of your tow vehicle as part of the wiring. Newer vehicles use a "five wire" configuation to send signals to the rear lights, whereas most trailers use a "four wire" lighting set-up and aren't compatible without the converter box. The fifth wire's signal is converted inside that box to allow four wire trailer lights to function properly. These tail light converter boxes are available at any auto parts store, right off the rack. The clerks at these places will know what you need and they can cross-reference the right one for your vehicle. Most of them just plug right into the existing wiring harness, but occasionally you may have to make the connections by hand. Should run about $15-20.

If this is not the case (if you already have the converter,) we may need a bit more info/background on the vehicle and trailer to advance your troubleshooting.

All grounds will ground to the frame. The 7-pin connector also should have a ground wire which runs between the trailer and the tow. Normally, even though there are seven pins on a seven pin connector, most people wind up only using six of them. The seventh is used if you want to hook up reverse lights, but most trailers don't have them. My Casita does, but I never bothered to hook up the reverse light circuit.
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Old 10-07-2010, 05:54 PM   #5
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Trailer: U-Haul CT
Posts: 62
The lights are on the trailer.

The tow is 2010 Nissan Frontier
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Old 10-09-2010, 08:30 AM   #6
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Trailer: 1981 Trillium 5500
Posts: 1,118
usually if you have red and black wires coming from a fixture, they are running and signal wires.

Red is turn signal (yellow lights), or brake light(red lights)
black is marker ( or running light)

You also need a ground wire running to a mounting stud on each light frame if there isn't one there already.
This is typically a white wire.
the easy way to wire these are; hook the two black wires together, hook the red on the red light to your brake wire, hook the red on the orange light to your signal light wire, make sure there is a ground right to the taillight frame (metal)
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Old 10-09-2010, 10:19 AM   #7
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Trailer: Toyota Sunrader and 16 ft Scamp
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George is correct
Most Asian label vehicles need an aftermarket tail light converter to convert the 2 bulb system to the single bulb domestic system. It's smaller than a pack of cigarettes, cost about $20.00, is easy to install and is available most anywhere auto parts are sold.
After the installation you will have only 4 wires for from the vehicle to the trailer to operate your trailer lights. They will be ground, right turn, left turn and marker/ tail lights. Your brake lights will operate through your turn signal lamps.
Once you have your new connector wired correctly you can start sorting out the mess in your trailer.
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Old 10-09-2010, 11:26 AM   #8
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Trailer: U-Haul CT
Posts: 62
Thanks for the information. I going to get some time this afternoon to try this.
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Old 10-09-2010, 12:14 PM   #9
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Trailer: 1981 Trillium 5500
Posts: 1,118
here's the quick way if your frontier did not have a factory plug:∂=1183 84

this will make sure what's on the tow works, then you just need to get the trailer right

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Old 10-09-2010, 06:23 PM   #10
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Trailer: U-Haul CT
Posts: 62
Tow came with proper wiring. I got it working this afternoon. Thanks for all your help.
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Old 08-02-2016, 09:58 PM   #11
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Name: Kenneth
Trailer: Scamp 19'
Posts: 8
1991 Scamp 19'

To say that I am confused is an understatement! I was under the impression that there is a standard for wiring trailer lights. Today I attempted to replace the 7 pin plug on my Scamp 19' as the plug had a bad life and loose wires, from previous owner. I wired the new plug per the instructions that came with the plug, nothing works.There is conflicting information form Scamp as to how the plug should be wired. Any help would be greatly appreciated.
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