ramps 1.4 has afaik 2 conectors for each of the Z axis motors. just conect each individually. or, if you want to torture yourself here is the link: Have fun!by zegwadekh - Mechanics
What works for me is to send it home after every layer. Currently in repetier host this option is only available for slic3r. just put G28 X0 Y0 in the "Layer change G-code" in printer settings of slic3r. my Y has a max endstop, which made me question about if it would work at all, but it does. Adds few minutes in total printing time, but reduces reprints by 100% so far.by zegwadekh - Ormerod