My dad just bought a bass boat (think it's a Javelin) with a 150 Johnson.  When you try to raise the motor or adjust the trim, it blows the fuse.  It's been to several dealers, who all seem stumped.  It blows them immediately if you raise the motor, but is intermittent lowering it.  Also, the tach doesn't work when this happens.  The tilt motor housing is clean and does not appear corroded or damaged.  Any ideas why this is happening?  

sounds like a short. Now its time to do that fun task of checking all your wires and connections to make sure something isn't shorting the sysytem. and make sure they are hooked to the right spot. I wouls start with the trim wires since it happens when its being used. also check the switch, maybe it has short.

Just to clear one thing, a 97 Johnson is not a Ficht. Only the Evinrudes were made as Ficht's.

To Trouble shoot your problem, I would start by unplugging the tilt and trim motor and see if it blows the fuse then. Natuarly it's not going to move but if still blows the fuse, that will tell you if it's the not the motor but the relay control. I would then unplug the up relay and try it. Might try unpluging the control control cable going to the boat and just try it from the side of the motor.   Try to isolate exactly what circuit is blowing the fuse. I would also bypass the up limit switch, make sure it's not shorting. On the 150's, there was some sharp casting edges around the top of the block where the cable harness runs, check and make sure they haven't eat into the harness and causing a short.