best to run new power and ground wires straight to the cranking battery, don't use the TM battery as it will cause interference when the TM is in use. Try and keep the two sets of wire seperate as best you can, or cross them at 90* angles if you have to. If you can't run seperate wire, consider getting a small 12v batt (riding mower battery) and hooking the FF up to it if you have room in the front of the boat for the small batt.
GO BIG ORANGE !
I meant to behave, but there were just way too many other options available at the time.