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Tail lights stop working when I put my headlights on

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I just recently bought in 1979  Chevy K20 Fleetside. All my lights work until I turn on my headlights then j the brake/turn signal reverse lights stop working or are super dim. I took apart the wires and cleaned them up made new connections and fastened under frame. I checked all fuses and circuit tested. I can not find what my issue is please if I have any suggestions I'm all hears. 


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