Back Brakes won't bleed

A couple weeks ago my brake lights got stuck on, crawled under dash and noticed the brake pedal was not coming back far enough to hit the switch. It seemed that the brakes didn't feel quite right so I decided to bleed them. I started with the passenger rear. My Dad pumped brakes up I turned the bleeder valve, and no fluid came out. Went to drivers rear, and same thing. I decided to go up front (My car has the factory non power discs up front 1971 Dart) brake fluid came out fine.

My car has new master cylinder, and new shoes front and rear. The work was completed three years ago, and I have never had any problems. Does anyone have any ideas of what could be wrong? Is the stuck switch issue related?