k1100rs motorcycle abs warning light

I currently ride a 1996 k1100rs motorcycle, and keep having the tail light (rear brake) test light flickering and and lighting while riding. It goes out when you tap the rear brake pedal, but then begins to flicker and light shortly there after. The front brake will drag a little if I don't push it back. But, I discovered if I let it drag enough to light the brake light, it will keep the test light from lighting. I replaced the pads on the front and bled the system, but that didn't help. does anyone know what is causing this? It did not do this when I first got it.