Hey fellas,this may seem like a silly question but I dont want to fry my unit. I bought a new boat. I"m putting my Marcum LX-5 on it. I found a hot red wire to hook to under the steering column. My question is which black wire am I safe to hook to. can I go off of any ground wire or do I need hook to a specifec. Again,sorry for my ignorance and thanks for your help. Jason