Fisherfinder Electrical Problem

[MOBass]

When going through the boat to make sure everything was functional I found the bow fishfinder would not turn on.  I took the bow panel apart and got out the trusty meter and tested everything.  I found power all the way through the chain to the unit, but it would still not turn on.  I unhooked the unit from the bow and ran touched the power cables directly to the battery and it turned on just fine.  Reading same power at bow as at the battery.  Fuse appears good.

Anyone have an idea on what is causing the unit not to turn on even though I am reading power to it?  

 

My shortcut to get fishing again is to run a new power cable and see if that does the trick.  I plan to 'bench test' it by laying the cables from battery to bow and hooking up the finder to make sure it runs before fishing cables under the deck. 

[fishinwrench]

When you are checking for voltage at the bow harness are you also testing for a good ground connection at the harness plug itself ?

[MOBass]

 

When you are checking for voltage at the bow harness are you also testing for a good ground connection at the harness plug itself ?

How would I test for good ground?  

I am dumb when it comes to electrical.

[fishinwrench]

One of the pins in the harness is a 12v positive, and another pin will be the negative side of the power circuit.  Both need to be completed circuits. 

If you were catching a ground somewhere other than the sonar units harness when you tested for voltage then you truly haven't tested the complete circuit that powers up the sonar unit, you only tested 1/2 of it.

Make sense?   

[MOBass]

Yep, went to the pins on the plug that go into the unit.  I started at the battery, went to the harness under the bow console, and finally to the pins on the unit.  All read virtually the same.

I took the unit off and touched the power cables straight to the battery terminals and the unit turns on.

[fishinwrench]

That's a head scratcher.  If you have 12v at the pins then it should power up.

[Quillback]

Maybe check and see if polarity is reversed if you haven't. 

[MOBass]

 

Maybe check and see if polarity is reversed if you haven't. 

Double checked that.  It had worked fine for three years so everything was hooked up right, but I did double check to make sure nothing weird was going on.  I also pulled another unit out of storage and checked it.  Same deal, no worky at the bow, works fine direct connect to battery.

Someone suggested that there might be a bare spot on the wire and when a load is put on it is loosing voltage through the bare spot contacting something.

I plan to run a new power cord and bench test it along the way to make sure it works.  If that works and gets me fishing I will deal with it when I have more time.

[fishinwrench]

I have run into issues with the cheesy 3-5 amp fuse links getting corroded.  The pins will still show 12v on the voltmeter but will drop voltage when the circuit is put under a load.       If there is a fuse link in-line you might pull it apart and clean the contacts with a wire brush.

[Flysmallie]

Even if it's not a cheesy link Wrench makes it a good point. It sounds like corrosion. I've seen the same thing happen with a corroded fusible link. Corrosion in the wire would do the same thing.