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Determining Correct Wire Power Wire On 3 Wire Marker Lights


We’ve purchased marker lights for our fibreglass camper with 3 wires white, black and yellow. We presume white is ground and black matches to the brown continuous. Some people have suggested yellow or black may relate to the intensity of the LED light, ideally we want it at its brightests. We got the tailights working correctly, but the marker lights still wont light up…. Any Advice? PS given the fibreglass set up, instead of grounding at each marker location, weve run a ground cable around and all 4 marker lights including tailights are tied into it and its grounded at front of the trailer.


Expert Reply:

I would be happy to help!

It sounds like you got marker lights that have a turn signal function as well.

What you will need to do is ground the light to the frame of your trailer and touch the black wire to the positive terminal of a 12v battery and then do the same with the yellow. This will tell you which light is the brighter light that is used for running lights.

Now you mentioned that lights do no turn on so you will need to turn on the headlights of your tow vehicle and use a circuit tester like # PTW2993 to test the wire feeding the light to see if it is getting power. If it is not getting power make sure your connection from the light to the trailer wiring is secure.

If you have power but still no lights, the issue is your ground. Each light needs its own individual wire going to the frame of the trailer.

I included a link to a helpful article on trailer wiring for you to take a look at.

expert reply by:
Samuel C

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