phantom voltage?

alumacraft fisherman 160 tiller. Found an unused pair of wires in the bow that come from the same loom as the bow light. Tested them with the multimeter, 11.9v. Started installing a cig plug / usb charger up in the bow, got it all connected, nothing. Disconnected the cig plug, tested the wires with the multimeter again, now I can’t get a reading at all. Followed the wires (orange and black), they run under the rod locker in the center of the boat, then back to the main loom behind the livewell. Low and behold, these wires are not connected to anything back there

So my question is — how was that multimeter reading 11.9v when I first tested these wires?

And my second question — would it be a big no-no to run a small accessory like a cig plug to the deep cycle in the bow? This outlet will be used occasionally to charge a phone and sometimes to run the Engel aerator. Only other thing on that battery is the trolling motor (12volt powerdrive v2).

Appreciate the feedback.

Those wires have to be going somewhere, or piggy backed into something.

Did you happen to have power when the key or master power was on? Or while some other accessory was on (like the bow lights)? And not when they were off?

As for hooking an accessory to your single tm battery, absolutely no harm in doing so.

EDIT: forgot to mention, there is no key or master on/off. And nothing was on.

I traced the wire completely, it terminated in a butt splice that was taped off. Untaped it, added a terminal ring and connected to my starting battery, my new cig plug started working. Don’t ask me how in the world it was reading voltage before, but it was definitely not hooked up!

Thanks to the confirmation on using the TM battery. That was going to be my easy way out but I have it run properly to the cranking battery now.

Next big annoying thing is that the dang usb plugs glow blue at all times. Package didn’t mention that. So now I have to run a switch too, or I’ll have a constant draw on my battery. You think you’re doing something simple. I should’ve known that was wishful thinking.

If the wires in question were run parallel to another pair that were running something while you tested them they would show a voltage but no current because of induction.

Tom schmitt wrote:

If the wires in question were run parallel to another pair that were running something while you tested them they would show a voltage but no current because of induction.

They are in a loom parallel to the wires for the nav lights, that must have been it. It doesn’t matter that the lights weren’t on, or even inserted into their sockets at the time?

dirtywater wrote:

<div class=”d4p-bbt-quote-title”>Tom schmitt wrote:</div>
If the wires in question were run parallel to another pair that were running something while you tested them they would show a voltage but no current because of induction.

They are in a loom parallel to the wires for the nav lights, that must have been it. It doesn’t matter that the lights weren’t on, or even inserted into their sockets at the time?

No you ould need a current to produce the efect.

Well I’m stumped then. This is a really basic boat with not much going on at the cranking battery:

– Electric start for the 25 yamaha, that wiring is all back in the stern
– Nav lights, bilge, and livewell are all on switches and were all turned off
– Garmin 93SV is not switched, but I disconnect the transducer and power cables after every use.
– There is a common ground for all lights, bilge, livewell, and this extra unused orange lead that I’m using for the cig plug.

I’ve never had a single issue with anything electrical in this boat so I’m hesitant to start ripping stuff apart. But if there’s a sloppy splice and the bare nav light wiring was actually touching this other wire somewhere along the run, could that have been it?

I wonder if those wires are for a front trim switch? Does your boat have one up there?

CaptainMusky wrote:

I wonder if those wires are for a front trim switch? Does your boat have one up there?

No power T/T on this boat. I believe the wires may have been run when it was rigged to have the option of adding a fish finder at the bow.

Was the 11.9 V reading solid or was it drifting around?

Is it possible that your VOM has a “hold” function, and the 11.9V reading was from something you checked prior?

HRG

Ron F wrote:

Was the 11.9 V reading solid or was it drifting around?

Solid.

Hot Runr Guy wrote:

Is it possible that your VOM has a “hold” function, and the 11.9V reading was from something you checked prior?

HRG

I read it multiple times, watched it return to 0 after each time, and then read 11.9 again when testing.

dirtywater wrote:

Untaped it, added a terminal ring and connected to my starting battery, my new cig plug started working.

I’d strongly recommend an inline fuse as close to the battery as you can

marineman wrote:

<div class=”d4p-bbt-quote-title”>Dirty Water wrote:</div>
Untaped it, added a terminal ring and connected to my starting battery, my new cig plug started working.

I’d strongly recommend an inline fuse as close to the battery as you can

Yes, always — In this case I was just testing so I just crimped on a terminal ring. Final install will have the inline fuse, heat shrink, etc. Another dumnb thing is that the plug came with an inline fuse wired just inches from the plug itself — which will be installed 15 feet away from the battery.

bigfatcroixbaby wrote:

If you held a gun to my head and told me it’s my life or figure out an electronic gremlin I would’ve been dead years ago. I HATE electonics!!!

I actually enjoy it, at least in simple applications like this. There’s gotta be an explanation, I just haven’t found it yet. That’s fun to me.

To induce a current from one wire into another, either the current has to be fluctuating or the distance between the wires has to change. The first one is a transformer, the second one is how a generator works. Running DC through a wire won’t induce current into another conductor unless something changes.

Seeing that 11.9 volts on a voltmeter can be deceptive. A good voltmeter has an extremely high internal resistance. And in a circuit the highest voltage will be across the highest resistance. Yup, Ohm’s law. That voltage might look solid on a voltmeter but it might also disappear if you placed a load there, like a light bulb.

I know you don’t want to hear this but my guess is a bad spot in the insulation or a pinch point where that wire is making a poor connection to a wire that is connected to the battery.

SR

Steve Root wrote:

That voltage might look solid on a voltmeter but it might also disappear if you placed a load there, like a light bulb.

The voltage disappeared after I connected the cig plug accessory. The plug had an always-on blue glow that lights the USB ports, so that could’ve acted as a load when I connected it?

Steve Root wrote:

I know you don’t want to hear this but my guess is a bad spot in the insulation or a pinch point where that wire is making a poor connection to a wire that is connected to the battery.

You are probably correct. In the next couple years I’d like to replace the carpet with vinyl or knockoff seadeck stuff. I’m hoping to replace the wiring when I have the floor up. Fingers crossed it can wait ’til then.

I am feeling kinda stupid. Putting everything back together tonight, the 3-way rocker switch for the nav lights was not off as I’d thought. So I think @tomdog was right on with his initial thought of induction causing the bogus reading at the meter.

Thanks everyone for chipping in your collective insight. Got everything all buttoned back up!