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What's this 3rd wire going to my boat's starting battery?

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I disconnected my boat's starting/cranking battery and when I went to put the new battery in I realized that there was a 3rd wire that seems to come from toward the front of the boat. 

 

I connected the 2 wires from the motor, red and black, and it worked. So I don't know where this 3rd wire (black) is from (left disconnected).

 

 

 Is it from the boat's battery gauge, and if it is, does it go on the positive or negative terminal? 

 

 

I know it's not for a charger as I have that disconnected. 

 

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What doesn't work on the front of the boat?  What do you have on the front of the boat?

 

 

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3 minutes ago, TheRodFather said:

What doesn't work on the front of the boat?  What do you have on the front of the boat?

 

 

 

 

I'll have to check. But wouldn't it need a negative and positive, not just one?

 

 

I believe the front depthfinder is connected to the TM batteries. 

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Hard to say, what type of boat is this?  Console with gauges, etc?

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DC circuit Black wires shouldn't be positive, it's more then likely a ground wire.

Tom

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Tracer or striped wire should be + Solid wire should be -

Red Wire should be + Black should be - 

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Possibly your dashboard grounded. Before you head out next, check ALL gauges, electronics, and lights. Make sure you always carry basic tools to fix this should the need arise when you are out there. I directly wired my music amp to my battery in my boat. Things that draw a lot of power are hooked straight to the battery. These things will be obvious when you do a systems check.

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1 hour ago, tcbass said:

3rd wire (black) is from (left disconnected)

Do you own a volt meter, or know someone that does? Check continuity from the black wire to ground. That’ll tell you whether or not it’s a ground.

 

Good luck.

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1 hour ago, tcbass said:

So if it’s a ground does it go to the negative?

Yes.  If it is a ground wire it would go to the negative terminal of the battery.  Is this an aluminum boat?  Does this boat have forward controls?  

 

(I take no responsibility for any smoke let out of your wires. People do some hack work to boat wiring!  Who knows what was done, if you aren't familiar with electrical you may want to have somebody look at it for you before something possibly expensive gets fried).

 

Best thing to do is find out what doesn't work, then start testing to see if it doesn't work because it's missing ground, or 12v.  You would need a DVOM, or a test light can work if you know how to use it.

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Thx for the help guys. I’m pretty sure it is the ground. 

 

I try try to always take pics of things before I dissemble them to avoid this type of situation and did but didn’t think it showed anything until I looked closer and realized it does show 2 wires on the negative. At first glance it looked like only 1 wire. 

 

 

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Good to keep the smoke in.  An electrical engineer once told me that most electrical and electronics devices fail because the smoke gets out.

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12 hours ago, tcbass said:

 

 

I'll have to check. But wouldn't it need a negative and positive, not just one?

 

 

I believe the front depthfinder is connected to the TM batteries. 

Never connect your depthfinder to  your TM batteries.

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6 hours ago, je1946 said:

Never connect your depthfinder to  your TM batteries.

 

 

Why not?

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You can hook up electronics to the TM battery if you only have 1 battery.

Ideally you want the electronics to run on constant 12V supply, not a supply that is going down in voltage with use, or pick up the OB's charging (altenator) interference. 

Tom

PS, put flat washers and a independant nut between the wire terminals, don't stack them using 1 nut. 

Tom

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49 minutes ago, WRB said:

You can hook up electronics to the TM battery if you only have 1 battery.

Ideally you want the electronics to run on constant 12V supply, not a supply that is going down in voltage with use, or pick up the OB's charging (altenator) interference. 

Tom

PS, put flat washers and a independant nut between the wire terminals, don't stack them using 1 nut. 

Tom

 

Should they be stainless or regular?

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21 hours ago, WRB said:

You can hook up electronics to the TM battery if you only have 1 battery.

Ideally you want the electronics to run on constant 12V supply, not a supply that is going down in voltage with use, or pick up the OB's charging (altenator) interference. 

Tom

PS, put flat washers and a independant nut between the wire terminals, don't stack them using 1 nut. 

Tom

 

 

Should they be stainless or regular?

 
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21 hours ago, tcbass said:

 

Should they be stainless or regular?

Stainless Steel or tin plated brass to reduce corrosion from the battery. It's also a good idea to coat the everything on the battery post with vasoline to further reduce corrosion oxides from biulding up. 

Tom

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On 6/23/2019 at 2:30 PM, WRB said:

You can hook up electronics to the TM battery if you only have 1 battery.

Ideally you want the electronics to run on constant 12V supply, not a supply that is going down in voltage with use, or pick up the OB's charging (altenator) interference. 

Tom

PS, put flat washers and a independant nut between the wire terminals, don't stack them using 1 nut. 

Tom

 

What's the reason for this?

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