trouble installing a multi-jamma...help?

I have a y-plus multi jamma and I want to install in my 4 slot mvs cabinet, so I have a choice by moving the harness to play neo-geo games or jamma games. I already got the neo-geo adapter from jammaboards, the y-plus 4 in 1 multi-jamma, and waiting on a longer jamma harness from Bob Roberts. Ok so I installed everything. When I use the jamma adapter on the multi-jamma I get no sound, and the right player works,but not the left(adapter works fine when used with one board,not with multi). When I take the adapter off and plug the multi right into the geo harness, sounds good looks great...but players controls or coin mech does not work(I had this problem with a jamma cabinet and had to make return grounds with jumpers from the #2 pad on the multi-jamma to the coin mech,and each player controls,that cab works great now!) So I make the jumpers hook one up to the coin mech,great it works,hook another jumper up to the right player,that works...now the problem...When I touched the jumper up to the right player controls I get a little feedback thru the speakers and see voltage from the jumper to the ground, but after the jumper is clamped on...no feedback and everything works good. So can I do any damage if I leave this hooked up like this,is this safe? Should I hook up the jumpers somewhere else...where? Is it safe to plug the multi-jamma or jamma board directly into the geo harness, I have done it and it works great, but is this ok to do? Thanks for taking the time to read this,sorry it is a long post....but I NEED HELP! Thanks! ~The Rookie~