Had to put my (bigger) deep cycle battery in the boat today, so I took some time to look some things over.

First, there are three things running off the cranking battery.  One is the flasher, don't know what the other small wires go to, and then the outboard.

Should it be that way?  I would think the flasher/fishfinder should be running off the TM battery rather than the cranking battery.

Second, I'm going to order a fishfinder this week.  Should I run the new electrical wires, or can I just splice into the existing Humminbird flasher power wires?

Third, when I install the fishfinder, should I put an inline fuse between the graph and the battery?  If yes, what size would you recommend?

I plan on using the existing transducer cable to pull the new cable through the boat.  I can do the new wiring then as well, shouldn't be much of a problem, but if the existing wiring will handle the load, I'd rather just leave it there.

Thanks...

yea my deepfinder is feed off of the cranking battery and yes you should be able to use existing wires and i would fuse the circuit if it isnt already......i would think a 5 or 10 amp would be good

I think you should run new wires. Your new sounder will most likely have a fuse and holder with it. If not the instructions should give you the fuse size. If I recall correctly the fuses to my sounders are 1 amp maybe 2 certainly not 5.

The reason you run the sounders from the cranking battery is that on occassion there is signal feed back from the TM to the sounder.

The reason you run the sounders from the cranking battery is that on occassion there is signal feed back from the TM to the sounder.

That makes sense.  I fired up ye old Humminbird flasher this morning just for kicks.  My FF (Humminbird PirahnaMax10 portable) x-ducer was on the other side of the boat.  Got a ton of interference.  Went from reading 18' to reading 370'.  Shut off the flasher and back to normal.  BTW, does anyone want or need an old Humminbird flasher?  

My only problem is that for every trip to a lake where I can use my OB, I'll make 4 or 5 trips to an electric only lake.  Guess I'll have to start throwing the charger on the cranking battery every few trips.

The only thing on the TM battery should be the TM.  Everything else gets hooked to the crank battery.

Considering the age of the boat I'd consider replacing the bilge pump immediately.  When you do that either get a new pump with an automatic on switch built into it or get one of the automatic bilge switches.  The pump should be hooked up with the hot wire from the bilge pump on/off switch on the dash and a second line should be run straight from the battery to the automatic switch.  Take it from someone who's sunk a boat because the auto bilge switch failed.  Check it often.

Bilge pump is pretty new.  I'd say 5 or 6 years old.  When I do replace it, it will be with an auto pump.