Fishfinder Wiring Issues

[dxs217]

My fishfinder has three wires (red, black, and small black (drain wire ground). The old fishfinder had the thick black negative wired to a plate under the helm. It looks like a ground plate with many black terminal connections. The drain wire ground (little black wire) was not connected to anything.

Do I need to connect the small black drain wire or does the big black negative to the ground plate suffice? Should I hook both of them to the plate?

I have a 1999 215DC.

Please elaborate, thanks in advance.

Dxs

[seabob4]

That bare wire is called a "shield".  It needs to be terminated to ground.  And that plate where your other grounds are terminated to is called a "ground bus"...

[dxs217]

Thanks Seabob. Should I ground both wires to the ground bus? Should I ground both wires to the same post or a different post?

Knowledge question: why does the system need a shield wire if the thicker negative wire is grounded?

Thanks

Dxs

[seabob4]

Thanks Seabob. Should I ground both wires to the ground bus? Should I ground both wires to the same post or a different post?

Knowledge question: why does the system need a shield wire if the thicker negative wire is grounded?

Thanks

Dxs

It's all about EMI, or electro-magnetic interferance.  Since indeed the shield does carry some sort of current, it needs to have a place to dump that current.  Here's a bit from Wikipedia...http://en.wikipedia.org/wiki/Electromagnetic_shielding

I'm no expert, and I didn't stay in a Holiday Inn Express last night, but I do know a bit about electronics, and how to ground them.

[dxs217]

Sounds good. I'll ground the shield and the negative to the ground bus.

[seabob4]

I usually just tie them together and use 1 ring terminal.  The shield is pretty skinny, so a 10GA ring works fine...

[dxs217]

Done and done.

System looks great. Had to remove windshield to mount it on helm but fits nicely. GPS timed right in. Won't get to do a water test until next weekend. Hopefully the transducer will work.

Is there a way to test the transducer out of the water? Probably not...

[flounderpounder225]

Done and done.

System looks great. Had to remove windshield to mount it on helm but fits nicely. GPS timed right in. Won't get to do a water test until next weekend. Hopefully the transducer will work.

Is there a way to test the transducer out of the water? Probably not...

Glad you got her all done, you can test the transducer in 12 and 16 oz cans of beer with the tops cut off, see if the depth reading is different??  :alien: Happy 4th.  
Marc

[seabob4]

Done and done.

System looks great. Had to remove windshield to mount it on helm but fits nicely. GPS timed right in. Won't get to do a water test until next weekend. Hopefully the transducer will work.

Is there a way to test the transducer out of the water? Probably not...

Some will read, some will just show the dotted lines...

Marc, what about a Fosters can?  Might as well get some variety here...  

[flounderpounder225]

Done and done.

System looks great. Had to remove windshield to mount it on helm but fits nicely. GPS timed right in. Won't get to do a water test until next weekend. Hopefully the transducer will work.

Is there a way to test the transducer out of the water? Probably not...

Some will read, some will just show the dotted lines...

Marc, what about a Fosters can?  Might as well get some variety here...  

Oh yeah.. I remember those bad boys from the cruise ship... 32 Oz... can.. you'd get a reading in those...