Heated Bed Issues (no replies)

I just installed a heated bed on my printer and could not get it to power at first. I increased the thickness of the wire coming from the PSU (12v 20A) and can get power to the bed but it interferes with powering the hotend. When I start the heated bed first, I cannot get power to the hotend, but when I start the hotend first then I can get power to the bed. I thought, "well fine I'll just have to remember that," but when I went to print, the hot end turned off while the bed kept on. For some reason, the x-axis did not stop when it got to its commanded position, so I had to reset the printer. When I did that, the hot end turned back on and heated bed turned off and the x-axis reversed direction towards home.

No idea what's causing this but could anyone offer some advice?

MEGA 2560, RAMPS 1.4, Sprinter, Repetier-Host, MK1 heated bed, 12V 20A PSU.