Tail lights stop working when I put my headlights on

[Jon Rush]

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. 

[riverbanks]

Power feed,weak?fusable link leaving starter, compromised?look for green fungus on end(s) of link or give it a wiggle while lights are on, either brighter or maybe no lights

[Jon Rush]

Thank you for the reply. I ended up finding a bad ground in the tail light housing. Cleaned it up and rewired it. I also purchased LEDs. Huge difference.