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Old 11-11-2013, 12:12 AM   #1
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Name: Jason
Trailer: Companion
Iowa
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Wiring trailer lights

I need to rewire all my trailer lights. I have a basic understanding of the flat 4 pin wiring system used on my trailer.

The white ground wire currently runs from the 4 pin plug into the camper and straight to the lights. Should I first connect this wire to the frame of the trailer and then run the ground wire to the lights???

I'm assuming the lights currently work because the white ground wire from the tow vehicles plug is grounded to the tow vehicle.

Is it really necessary to connect the ground wire from the trailer 4 pin plug to the frame first and then run it to the lights or is using the tow vehicle as my ground an acceptable way to complete the circuit?

Thanks in advance for your help!
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Old 11-11-2013, 08:29 AM   #2
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Trailer: 1996 Casita Freedom Deluxe 17 ft
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Trout, a wire seems like it would always be a better ground than the frame, which is open to the elements most of the time and can corrode over time. Grounding the frame of the trailer is probably a good idea too, just to make sure you don't have any stray currents floating around. But as a general idea, each point should have one (and only one!) path back to the battery.

Since you're rewiring your trailer, maybe this would be a good time to put an extra brake light on the rear of your trailer, mounted up high. I've always thought all our units should come with one.
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Old 11-11-2013, 08:37 AM   #3
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Here's a link to some decent info on "Correct" wiring color codes, but don't bet that either you trailer or TV's wires will match.

Trailer Wiring Diagrams | etrailer.com

To answer your questions:
1. Many trailer builders use the frame as the common ground for lights. While cheaper when building, this leaves a lot of opportunities for loose/damaged/corroded ground connections down the line. As a precaution, I always run an intact ground wire to the lights themselves.

2. You need to always run a ground wide from the TV, though the connector to the trailer. If you are running a charging line you also need to connect that ground to the trailers frsme, as well as to the lights.



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Old 11-11-2013, 08:38 AM   #4
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Trailer: 1996 Casita 17 Spirit Deluxe; 1946 Modernistic teardrop
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You need a continuous ground circuit back to the tow vehicles ground. It can be by the ground wire in the plug connected to the ground of every light on the trailer, or as is commonly done, using the trailer frame as the ground and each lights ground connected to the frame. With a fiberglass trailer the best option may be to run the ground wire from the plug to each light. The ground (white) wire on the tow vehicle plug is probably connected to a screw on the car body, which has a connection to the negative terminal of the battery, completing the circuit.
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Old 11-11-2013, 08:42 AM   #5
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Trailer: 1996 Casita 17 Spirit Deluxe; 1946 Modernistic teardrop
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Terry, interesting idea on the extra brake light, but how are you going to do that with a 4 wire flat plug. I have a rear bike rack, so I put an extra set of tail/turn lights on it.
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Old 11-11-2013, 08:45 AM   #6
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Name: Jason
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Thank you for the help I appreciate it!
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Old 11-11-2013, 09:20 AM   #7
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Quote:
Originally Posted by mary and bob View Post
Terry, interesting idea on the extra brake light, but how are you going to do that with a 4 wire flat plug. I have a rear bike rack, so I put an extra set of tail/turn lights on it.
m&b, that's a an interesting question. Obviously, the turn signals and brake light go to the same bulbs on the trailer, so that makes it rather difficult. However, there are devices available that take care of the logic needed to make this happen. Here's an example:

Adding a Third Brake Light to Trailer | etrailer.com
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Old 11-11-2013, 09:52 AM   #8
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Name: David
Trailer: 1978 Trillium 1300
Cumberland, Indiana
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Copied this from Command Accessories Website:

"If you are replacing an existing third brake light, the wiring harness already includes the proper wiring. However, if you are installing a third brake light where one did not exist before, you may need a logic module. Towed trailers do not have an electrical "signal" for the brake light. Instead, trailers traditionally use the same wire and light to indicate both a turn and a brake condition.

If your vehicle/trailer has separate red brake lights and amber turn signals, you will not need the logic module. Simply connect the new brake light to your brake light circuit.

If your vehicle/trailer uses the same red lights to indicate braking and turning, and your vehicle was not previously equipped with a third brake light, you will need a logic module for the 3rd brake light to function properly.

The logic module connects to the left and the right brake/turn signal circuit. When the brakes are applied, a signal is generated from the logic module which is connected to the third brake light. Installation is easy and the small logic module can be located in any convenient location."

Check this link:

Do You Need a Third Brake Light Logic Module?

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