Headlights and tail lights drawing to much power! Help

I have no clue what I'm doing when it comes to wiring so I need some help here. I have a 1975 plymouth duster with a 318 and the alternator reads fine and charges good when the lights aren't on but when I turn on my lights it drops to a negative charge and draws from the battery I have no idea what's wrong or how to fix it so can anybody help me figure this out it would be greatly apreciated!