behind the dash is a set of relays 3 when changing from trips to twins do i get rid of those. cant seem to figure how to wire in a twin harness

those are for the warning alarms. the one in the middle wqill probably be for the center relay. to track it down just trace the purple lead coming from each relay, or the tan with blue tracer lead, to the corresponding harness. it may trace to back of gauges or ignition switch before the harness. just depends on how clean the rig is still.. simply remove the leads to and from the alarms that stem from center engine relay.
if the boat is in mid rig just remove all power from boat and apply 12volts to the center engine purple using a makita style 12v cordless battery. the positive side. then a test light with jumpers or extendedleads to the ground of the 12v batt. and trace away,