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Dave Nova
Dave Nova, ASE Certified Tech
Category: Car
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Experience:  ASE Master Certification. GM World Class Certification
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I just wired a flat wire trailer harness for my boat trailer..petal

Customer Question

I just wired a flat wire trailer harness for my boat trailer. EWverything seemed to work, except when I turn on the truck lights and hit the brake petal, the trailer lights go out. I followed the directions. What did I do wrong?
Submitted: 3 years ago.
Category: Car
Expert:  Lurch replied 3 years ago.

 

Be sure the Trailer has a Good Ground from the vehicle
Just the Hitch will not always Ground the Trailer
You may have to attach a Extra Ground from the Trailer to the Truck

 

Try running a Good Ground from the Truck to the Trailer frame & try

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Customer: replied 3 years ago.
I ran a ground wire from the frame of the truck to the frame of the trailer and the problem remains the same. When I release the brake petal, the trailer lights come back on. Without the lights on, the brake lights work as well as the turn signals.
Expert:  Lurch replied 3 years ago.

 

If the Truck Lights are not affected & just the Trailer Lights go off, then there is a miswire, gorund or bulb issue in the Trailer

 

will OPT OUT & see if someone else has the wiring

 

 

 

 

Customer: replied 3 years ago.

I know that the wiring is correct; however, if what you are saying is that the only other possibility is the ground, I will replace all the ground wires and make sure that they are good. If this solves the problem, I will gladly accept your answer. I should know soon after lunch.

 

Thank you,

Pete

Expert:  Dave Nova replied 3 years ago.
Hello, My name is XXXXX XXXXX I can help you with your trailer wiring problem. This does sound like a ground problem. Make sure each of the trailer lights are properly grounded to the trailer. The ground is quite often made through the mounting bolts, so scrape away any paint around the mounting bolts so that it gets a good ground. Also on the four wire plug, connect the white wire to the frame of the trailer so that it gets a good ground from the vehicle harness. This should fix the problem.
Customer: replied 3 years ago.

Hi Dave,

 

I ran a new ground to each light from the frame of the trailer. I ran a ground from the frame of the truck to the trailer as well as the white ground harness wire. My ATV trailer worked fine on the old truck end of the harness, but I decided that it might be the problem, so I wired thenew truck harness from the trailer light package in hopes that it would solve the problem; however, when I apply the brakes with the lights on, the trailer lights still go out, but not on my ATV trailer.

 

Pete

Expert:  Dave Nova replied 3 years ago.
The problem may be in the bulb socket itself. Check to make sure the correct bulb is installed ( dual filament ) Also check to see if there is a good connection between the bulb and the socket for the ground. If you have a test light, check from the trailer frame to the bulb socket to see if the test light will power up. If it will not, then you still do not have a good ground at the frame. If it will power up then your frame has a good ground, but it is not getting to the bulb socket.
Customer: replied 3 years ago.

Hi Dave,

 

When I test the light sockets after applying the brake, I get nothing anywhere on the trailer, but before applying the brake, I have lights everywhere. The brake light works without the lights on, and the lights work without the brake on. Therefore, I know that it is not a bulb issue. All grounds have been replaced and are attached to bear metal on the trailer frame as well as the truck frame.

 

Pete

Expert:  Dave Nova replied 3 years ago.
Turn on the lights and have someone apply the brake. Then test for power on the brown, yellow, and green wires at the trailer. You should have pOwer on all three of these wires. Let me know what you find
Customer: replied 3 years ago.
I did that and I have no power on any of them at the trailer lights until the brake is released.
Expert:  Dave Nova replied 3 years ago.
Ground the test light to the truck. Then test at the trailer connector on the truck Test for power with the lights on and brake depressed. Let me know what you find.
Customer: replied 3 years ago.
I id that as well and I have power on all three lines out of the truck.
Expert:  Dave Nova replied 3 years ago.
Move the ground connection of the test light over to the trailer frame and retest the lines coming out of the truck. Let me know what you find.
Customer: replied 3 years ago.

Hi Dave.

 

Sorry about the delay, but I had to work today. I moved the test light to the frame of the trailer where the ground bolt is and I am only getting 4 to 6 volts from the three lines from the truck.

Expert:  Dave Nova replied 3 years ago.
Looks like you are still not getting a gground to the trailer frame. You did have full voltage with the tester grounded to the truck and now low voltage with the tester grounded to the trailer, this shouws that the trailer ground is bad.
Dave Nova, ASE Certified Tech
Category: Car
Satisfied Customers: 18888
Experience: ASE Master Certification. GM World Class Certification
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