Phaz,
where are the power leads hooked up for the finders.
you want to make sure that you run a clean positive and neg. wire to them.
I have installed a relay (wired to the key switch, but the clean power came off the battery. contact coils worked off the key)in a few boats and its worked pretty good.
some nitros need them due to the type of keyswitch they have. when the lights and livewells go on the screen pulsates.
rangers are generally pretty good.
Delw.