I haved an eagle doing the same thing. I already re-wired it from my trolling batteries to the cranking battery, but whenever I start the TM the sceen goes blank. Looks like I might have to make a portable transducer bracket and take the transducer wire out of the coily wire on my MinnKota Powerdrive trolling motor.

BTW, I did raise the sensitivity and start getting readings with fish and structure Thursday when I was fishing. Mine is probably good enough to leave where it's at. Try that first.