There are resistors that you put on your trim pump...no ground issue, you can run grounds all day long,nothing is going to change. The Part number is #8M0034258 this is a Mercury Marine part you will need 2 and here is a picture, again you don't have to redo any of your wiring unless its just not done properly...
Keep us posted

try installing a stiffening cap on the power side of your amps, they are likely pulling too much power from the overall system!!! assuming of coarse your grounds are all ok...