Garmin fishfinder mystery

The first picture shows the voltage at my FF battery, and in the second picture the same voltage is measured at the end of the cable that is inserted into the FF. That would seem to me to show that there's no problem with the wire from the battery to the FF.

The third picture is of the plug about to be inserted. The fourth shows what happens when the cable is plugged into the FF and I push the power button. Precisely nothing happens (not the most exciting picture...).

Of course, I figured the FF was bad. But, just to be sure, I stopped by Bass Pro Shops and plugged it into the same type of cable there, and it worked fine.

I'm baffled. Does anybody have any ideas as to what could cause this?

Possible that you are getting voltage but no amperage.  Can happen with old or worn out batteries.  Pretty common actually.  Normally the voltage would be lower.  Yours is quite high.  Maybe too high for the Garmin?

I just got mine in mail yesterday,and am installing right now. Let's troubleshoot this lil monster. Are you holding down power button longer than 3 secs? I did have to really push that sucker in tight and it only goes in one way. Could try a lower voltage going in,  don't think would matter thou. Check for any kinks in the wire, take air compressor and really clean those connectors. Hope yah get working.

You are within the spec of voltage per Garmin.  Down to either a pin not making contact between plug & head or lack of amperage getting thru to power up the head. 

From your testing I would say either that battery or the Cable. Since you tested at the store with their cable I would lean that way. Hook up to another battery to eliminate that battery. Car battery would be fine if that is all you have.

Garmin says that a voltage greater than 33v will cause damage, so I'm thinking that 14v should be OK. And I just replaced the cable, since I thought that must be the problem. I'll try hooking it up to a car battery...

Curious minds want to know...

Sorry for the delay---got distracted by this annoying thing called "work".

After literally dissecting it, I found that the problem was not the battery or the FF, but was instead in the cable. Likely due to overheating the sheathing when doing the heat shrink tubing. I cut out and redid the problem connection, and all is well.

Anyways, still seems kinda strange to me that the voltage was OK at the FF, but no current would flow.

Holy shit...

I literally just did your same exact troubleshoot with a new lowrance and posted 11 minutes after you!!

this is one of the weirdest incidences I've ever seen.. the postings!  probably took me 15 mins to write my post at exact same time as you.  weird

I have had to replace that same cable three times on my echo 500. The salt eats the female terminals in that plug really well.

Sorry for the delay---got distracted by this annoying thing called "work".

After literally dissecting it, I found that the problem was not the battery or the FF, but was instead in the cable. Likely due to overheating the sheathing when doing the heat shrink tubing. I cut out and redid the problem connection, and all is well.

Anyways, still seems kinda strange to me that the voltage was OK at the FF, but no current would flow.

Nailed it!  Lack of current!!!  I see this happen all the time for a variety of reasons: installation, corrosion, battery, etc.  Lack of amperage or clean power accounts for far more issues than the actual unit itself.

Wow...

So it looks like I will rebuild my connection even though I'm getting great voltage and see if that helps me.

I have no heat shrink connections but do have a little green corrosion on my marinco plug

good on ya for figuring that out!