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Getting Side Marker Lights to Function as Turn Signals and Running Lights  

Question:

Im re-wiring my trailer. It was a 4 pin flat connector in the past and Im upgrading it to 7 way connector with a junction box and Ill be adding brakes also to the trailer. I added amber lights on side of the trailer stl72ab for running lights and operate as turn signals as well. I replaced the rear tail lights and added couple more tail lights in back stl72rb to function as running lights, turn signal and brake lights. When you plug this 7 way plug in my truck hook up the tail light signal and brake light signal both come out the green wire of the 7 way cord which goes to my junction box. So now, wiring up the lights on my trailer they all operate correctly, running lights, turn signals, and brake lights for the red lights. But my issue is the amber lights lighting up for the brake light. My question is how to wire it so the amber lights are just for running lights and turn signals. How to wire them so they will not light up when braking, Thank You... My truck came from the factory with the 7 way connector on the rear. I did not install that. Thanks...

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Expert Reply:

Trailers use what is called a 2-wire system which means the turn signals and brake lights are on the same circuit. When you try to add separate amber turn signals you will need to separate out the brake light signal using a converter, # 118158.

On this converter the yellow input wire is for the combined left turn signal and brake light. Green is for the right turn signal and brake light. White is ground. On the output side the yellow wire will be left turn signal only, green is right turn signal only, and red is brake lights only.

If the side marker lights on the trailer that you want to function as both turn signals and marker lights have two separate input wires and one ground (either a separate ground wire or ground through the mounting hardware) then all you would have to do is run the appropriate output wire from the converter to the light. The running light circuit will bypass the converter and go to the lights like normal.

If the marker lights only have a power wire and a ground it is a little more complicated and I am not 100 percent there it will work but: From the output side of the converter the turn signal wire would go into 1 input on a diode, # RM-792, and the running light wire to that same light would go to the other diode. Then from the output side of the diode a wire will go to the power wire on the light. The only thing is that in this situation I am not 100 percent certain that the turn signal will override the running light signal but in all likelihood it will not.

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Michael H

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