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Trailer Connector has 4 Pins But 5 Wires

Question:

Hi - I have a Toyota Tundra and am trying to replace the 4 prong 5 wire connector with a 4 prong 4 wire connector. Ive combined the 2 brown wires together and hooked everything up. Everything works fine except when I apply the brakes while the taillights are on, the left taillight goes out as well as the taillight. When I release the brake, the taillight goes back on. The brake lights and blinkers work fine except when the taillights are on. Right side works perfectly no matter what - just the left that Im struggling with. I assumed that I could splice the 2 brown wires together it looked like they went to the same prong on the 5 wire connector but maybe thats not the case, so any idea where I could have went wrong? Do I have to order the flat 4 with 5 wires or is there any way to make the 4 wire connector work?

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Expert Reply:

I am a little confused as to were the connector is, on the truck or on the trailer. Brown wires are typically associated with running lights. If there are 2 wires coming out of that pin and we are talking about the trailer side then you have what is called a wishbone harness. It will still function exactly the same as a regular 4-wire 4-Way connector. It just has 2 running light wires to run to the 2 sides of the trailer to limit the amount of splicing you have to do.

If we are talking about the truck side I am not sure why you would have 2 wires on the running light circuit unless that is just how the truck is set up. But if it has a 4-Way, whether it is 4 wires or 5 wires, then the circuits have already been converter (combined turn signals and brake lights) so no additional cutting and splicing should be required.

Apart from all of that it also sounds like there is a short and a possible ground issue. A short could occur during the cutting and splicing process if any copper strands are touching another pin they shouldn't be touching.

Ground problems normally show up when there is more draw on a system such as when you have the running lights on and then use another function like a turn signal or brake light.

Make sure that the vehicle side and trailer side connectors are clean and free of corrosion inside and out. The main connector grounds should be attached to clean and corrosion free bare metal surfaces.

The light grounds should also be attached to clean and corrosion free bare metal surfaces. If there is anything between a light ground and the metal trailer frame or if the trailer has an aluminum frame, tilt bed, or folding tongue, any of these things can interrupt the ground. Running jumper wires from the light grounds to the main trailer connector ground can help.

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