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  #1  
Old 11-27-2009
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Quick wiring question

All of my technical books are still packed from our move. Please help refresh my memory. Marine wiring isn't the same as home or automotive wiring if I remember correctly.

NOTHING electrical that runs through the main switch bank is working. The master breaker does work. With a DMM, I traced power running from the battery, through the master breaker, through the individual switches, through the fuses, and out to the individual "load" wires to those loads.

Since there appears to be "hot" for everything, the only thing I can surmise is that a master ground is messed up somehow. On boats, how is the circuit completed? What does the (-) wire of the loads go to? A master ground that the battery is connected to?

Attached is my crude diagram of how things are wired to the switchbank.


Last edited by BubbleheadMd; 11-27-2009 at 07:24 PM. Reason: Attached diagram
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Old 11-27-2009
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normally there is a ground bar, it connects to the motor. from the motor then it goes to the neg post on the battery.

now some boats the ground bar is directly connected to the battery, and the motor is either directly to the battery or the bar.

you just need to follow the line from the neg post to see where it goes, it will eventually reach a ground bar.

sometimes it will be left disconnected when the batteries are removed or disconnected for the winter, or testing or some other reason
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Thanks Scottyt, make sense. The ground cable disappeared under a pile of fenders and stuff back in the well that they live in. I'll pull that crap out and check.

I have an outboard, but I'm sure there's a ground bar in there somewhere.
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Old 11-27-2009
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If you have an outboard it may go directly to the battery negative post - in any case that is where it has to end up.
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Old 11-29-2009
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What are you using for a ground when checking for voltage?

Most stuff I install have a + and - wire.

If you just check at both sides of something and you don't have a ground you can't check voltage can you?

I keep two 25 foot 14 gage wires (one red and one black) with clamps for trouble shooting.
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Old 11-29-2009
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Normally two wires run from the swich box to the apparatus you are using. One of them (the + one) passes through the switches and the other (- one) is connected all together to some bar or bolt behind the switch box. Most probably The line connecting these negative ends to the negative terminal of the battery is faulty. First check that bar or bolt.
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Old 11-29-2009
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MiTiempo- I have an outboard. It's pull-start and totally isolated from the boat's electrical system. It has electric start capability but it isn't connected.

Timebandit- If you put the DMM on each lead of an accessory, you should be able to read the voltage without your jumpers because one lead should be hot, the other should be ground. The DMM reads across the complete circuit. You do have a good idea though, a long wire connected to the battery (-) post, and the DMM connected to it, and the (-) wire of the accessory can be used to make a continuity check. If the meter reads "open" or "infinite" resistance, the accessory isn't grounded. If it reads "0" or "short" then the ground part of the circuit is intact.

Celenoglu- I believe that you're right. I finally got the boat to it's berth today so I'll finally be able to work on it.
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So here is a more complete sketch of how things should be...if I can find the grounding bar or whatever it is:
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Bubble, you're on the right track. With a DMM your are most likely measuring between a hot lead and a known ground ie the bus bar. This measuring potental V across the curcuit. If none of your DC curcuits work it is almost curtainly a ground problem.

And fyi , Household curciuts are AC and completely differant when trouble shooting. Automotive curcuits are DC and very similur but most automotive curcuits are run with a single power wire and grounded at the source so no return wire
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