Sorry it made sense when I wrote it, seems vague at the end. If you use a volt meter (dvom) set at 20 volts, black lead on the trailer frame and red lead in or on each contact in turn and you get 12 volts, then hook the black lead on the light housing and you should get the same voltages, if not then the ground to the light housings are suspect. Run a jumper wire to the frame and see if it works, if it doesn't run the jumper to the trailer harness at the tow vehicle plug if it works now then the problem is where the trailer pigtail is grounded to the frame of the trailer. Don't ever trust the hitch ball for a ground connection. Hope that helps. Les
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