HELP electric problem

[babbyblue66]

I have a 66 chevy stepside now what happened is my head lights will only work on high bean the low beam setting just turns off the lights but when the high beams are on it seams to draw off the battery more then the alt can handle and slowly kills the battery before some one asks the battery has checked out and the alt as well could the hole problem be the dimmer switch?
Ive tryed everthing i can think of now its time pick you brains so i can fix this