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Author Topic:   Boat Trailer Wiring
mauigirl posted 08-03-2007 12:33 PM ET (US)   Profile for mauigirl   Send Email to mauigirl  
Hello all. I want to rewire my old 18' trailer, but [I] need some help and advice. I have a flat four connector on my truck and trailer I want to pull out all the old miscolored wires leading to both tail lights with new wires. Since you know that I only have one wire of each (brown,yellow,green,white) and two sides of my boat, do I split the yellow with two separate wires where my trailer splits off to the tail lights? And then split the brown wire with to seperate wires to run to both lights? And then split the green wire with two seperate wires to run to both lights? And so on. Right now on my left side of my trailer has only tail lights and on the right side I have blinkers and brake lights but no tail lights, so I bought a pair of [B]lazer seven function tail blinkers brake lights. They have only a brown and yellow wire. I hooked one up and still no tail lights. I hooked up the left side and had again had only tail lights, but went from a three wire light to the [B]lazer which only has two. When the black wire not being used from my trailer hit the frame I had a spark and the light went out and now does not work.

I just want to start over, but [I] want to make sure I have the right idea as far as splitting the wires to each side. HELP. THANKS TO ALL THAT REPLY.

Casco Bay Outrage posted 08-03-2007 01:33 PM ET (US)     Profile for Casco Bay Outrage  Send Email to Casco Bay Outrage     
You are on the right track.

The easiest way to rewire is to get a new harness. This includes the 4 way flat connector and the wires. The split is taken care of at the connector.

If you do the wiring yourself, any connections, splices need to be sealed/waterproof.

You may want to save yourself some hassle and get the whole lights/harness kit. They run $35-70. Any boating/trailer/rv/rental place will carry them.

where2 posted 08-03-2007 11:01 PM ET (US)     Profile for where2  Send Email to where2     
Do yourself another huge favor, get 3 conductor wire and run it to each rear light independently. That way you can use one of the conductors to run the GROUND back to the vehicle connector rather than relying on the trailer frame to make a decent connection.

Each rear light typically requires two wires (Brake and Turn). They typically rely on a bolt coming out of the light to provide a ground to the trailer which gets picked back up again near the trailer coupler. Most problems are related to this lousy ground connection.

I propose to run 3 conductor wire to the back so you can provide a copper grounding path from the flat four connector at the hitch to the light at the rear. This eliminates using the trailer frame as the ground conductor. In my case, using this methodology has more than doubled the probability that my lights will operate correctly when I go to use the trailer.

mauigirl posted 08-03-2007 11:03 PM ET (US)     Profile for mauigirl  Send Email to mauigirl     
THANKS FOR YOUR REPLY;; I have the new flat 4 way harness,but my confussion lies in the yellow wire. Is the blinkers. So how do I get blinkers on both sides without splitting the yellow wire and so on with the tail lights and brake lights since the harness has only one yellow and one brown are you saying that the brown and white wires go down one side and the yellow and green go down the other for the blinkers tail lights and brake lights? Yes I bought the kit the harness is 25' long with just 4 wires (yellow,brown,white and green) so those 4 wires will run all my lights without splitting any wires since the lenght of the harness is 25'. THANKS


Chuck Tribolet posted 08-04-2007 12:49 AM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
Brown is tail lights and running lights. It needs to be split
and run to each light tail light, the side running lights,
and the "over-80" lights under the boat.

Green goes to the right side stop/brake light.

Yellow goes to the left side stop/brake light.

White is ground and should be split and run to every light.


Henry posted 08-04-2007 01:30 AM ET (US)     Profile for Henry  Send Email to Henry     
My trailer wire harness has a yellow, a yellow brown, a green, a green brown, and a white wire. This allows you to have a green and brown wire on the right and a yellow and brown wire on the left. Look closely yours should be the same or you got the wrong item. The white wire from the harness is ground to the trailer up front (do not route it to the rear with the green, yellow and brown wires). The green wire is the right stop and turn signal. The yellow is the left stop and turn signal. The brown wires are the tail, license and side marker lights. The license plate bracket goes on the left.

The light on the right has a green and a brown wire and a white wire with a ring terminal. The light on the left has a yellow wire and a brown wire and the white wire with a ring terminal. Put the white wire from each light on one of the bolts that fastens the light to the bracket. Make sure that there is no rust or corrosion on the brackets where you bolt the white wires so you have a good ground. Use sand paper or a file if necessary to make sure the white wires touch bare metal.

On the right, crimp (use heat shrink tubing) the green wire from the light to the green wire from the harness and the brown wire from the light to the green/brown wire from the harness (if you have side marker lights take the brown wire from the right marker light and crimp it together with with the green/brown wire from the harness and the brown wire from the light.)

On the left crimp the yellow wire from the light to the yellow wire from the harness and the brown wire from the light to the yellow/brown wire from the harness. Same thing for the left marker light as you did on the right.

That's it!

mauigirl posted 08-04-2007 02:57 AM ET (US)     Profile for mauigirl  Send Email to mauigirl     
Thanks for all your help all replies were usefull but when you say right and left is that looking from the back of the boat or the front looking back...Thanks


Tom Hemphill posted 08-04-2007 06:44 AM ET (US)     Profile for Tom Hemphill    
Left and right here presumes you are facing forward. Left = driver's side = port and right = passenger side = startboard.
Chuck Tribolet posted 08-04-2007 09:02 AM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
I would suggest soldering, then covering with hot melt glue
lined heat shrink tubing. Be sure to put the tubing on
before soldering, and slide it well down the wire away from
the hot solder joing. Wait till the joint is well and truely
cool before sliding it back and shrinking it.


jimh posted 08-05-2007 08:09 AM ET (US)     Profile for jimh  Send Email to jimh     
There are just three circuits in a typical trailer lighting installation:

--Running lights and clearance lights (brown)
--Left turn signal and brake light (yellow)
--Right turn signal and brake light (green)

Each of these circuits is fed by its own conductor from the wiring harness. The color code is shown in parenthesis above. All of these circuits use a common ground, which is the trailer chassis. A white conductor is used to connect to the trailer chassis from the flat four plug.


for some more guidance.

There are many trailer wiring kits available. It is impossible to say exactly what you have there on hand, so I will avoid any attempt at clairvoyance.

To easily wire a trailer get a quality wiring kit such as those sold by WESTBAR. The trailer side of the flat four connector will have FIVE leads, with two brown leads, one for each side. If you do not have a wiring kit like this, you probably have the vehicle side wiring kit. The gender of the connector will be wrong. Discard what you have and start over. See productID=4983&categoryID=209

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