Reverse voltage??

[tomxdana]

Mercury 125 hp 2002 Ser#ot509164. Trophy 1802 boat.
Was having trouble starting after lower gear oil change. (I just found out about pushing in on key for choke, new to boating) It cranked over twice and stalled. On the third time when I turned the key to on the gauges went backwards on the console. They don't read 0 they peg back the other way.

Full tank of gas reads below empty and battery gauge reads bottom of gauge even though battery voltage is 12.7. I think I have a ground problem. Cleaned up cables at the battery still have problem. I lost power to the trim switch on the cowl also so I assume that the problem is probably back at the motor end and not at the ignition.

I have a shop manual but it only includes wiring diagrams. Is there a way to get schematic for easier troubleshooting? I looked at the fuse and it looked good ( am going to ohm it out to make sure) Any ideas?

Thanks,
Tom

 

[Yepblaze]

Re: Reverse voltage??

Quite often meters will read askew till the motor starts.

for your tilt issue,
Start at the switch and test that first.

Schematics can bee seen in service manuals.

 

[hkeiner]

Re: Reverse voltage??

Teleflex has a good troubleshooting website. The "A Basic Gauge Test" one may be especially helpful to you.

http://ww2.tflx.com/tech.html

 

[tomxdana]

Re: Reverse voltage??

Not new to troubleshooting just to boating.. I'm actually an electronic technician. I'm used to using schematics. The Mercury shop manual only carries wiring diagrams. Normally when I turn the key to on my gauges work normally. I do this before starting to check fuel level and battery voltage. Now when I do it the needles peg the wrong way. Thanks for the replies. Any other advice.

Thanks,
Tom

 

[Willyclay]

Re: Reverse voltage??

Did you verify the polarity of the battery? I have a buddy whose 27ft sailboat stored in a wetslip with a solar-powered charger to run the bilge pump experienced reversal of polarity on the battery. He almost lost the boat to a fire caused by the event. Good luck

 

[tomxdana]

Re: Reverse voltage??

Boat was running fine on water. Took home on trailer and no other electrical performed on boat. Ie no new batteries etc... The motor did attempt to start twice. It was very cold and I didn't use choke. On third attempt is when problem started.

Thanks,
Tom

 

[Barnacle_Bill]

Re: Reverse voltage??

Look for a loose/corroded or open ground. Gauges often have a common ground and are wired in series.

 

[Silvertip]

Re: Reverse voltage??

When poor connections, particularly ground connections are present, current will take any path it can to get back to the battery. I suspect you have one or more bad battery cable connections. Don't just look at them. Disconnect both ends, clean them thoroughly (shiny bright) and secure them again. Now try it. If you need a boat diagram, there is a generic diagram at the very top of the Electrical forum.

 

[Silvertip]

Re: Reverse voltage??

Not to pick nits, but gauges are not wired in series -- the ground, 12V and lighting circuits are "daisy chained" and that does not make a series connection.

 

[Barnacle_Bill]

Re: Reverse voltage??

Not to pick nits, but gauges are not wired in series -- the ground, 12V and lighting circuits are "daisy chained" and that does not make a series connection.

The terms are pretty much used interchangeably in electronics,
Series and parallel circuits


From Wikipedia, the free encyclopedia
Electrical circuit components can be connected together in one of two ways: series or parallel. These two names describe the method of attaching the components, that is one after the other or next to each other.


Series (left) and parallel (right) circuits with two resistors and measurements of voltage and current.If two or more circuit components are connected end to end like a daisy chain, it is said they are connected in series. A series circuit is a single path for electric current through all of its components

 

[hkeiner]

Re: Reverse voltage??

I agree with Silvertip. Series and parallel wiring are totally different from each other and the terms should not be used interchangeably. Boat gauges are connected in parallel to each other.

However, a sender and gauge pairing (e.g., for a particular function such as a trim gauge or fuel gauge) are connected in series to each other. A sender's variable ohms resistance changes the reading on the paired gauge it is connected to in series.

This above is what I have always understood to be true. If am wrong, sorry for any misinformation

 

[rodbolt]

Re: Reverse voltage??

this aint rocket science. the are either in series,paralell or a series parralel circuit.
however the easiest way to check is to find the last ground in the chain and the last positive lead in the chain. then back up one meter lead until ya get to the start then the other.
most the time we track it back to a faulty ground.
daisy chaining actually DOES refer to a series circuit.
most the meters use a simple magnetic feild movement.
most the outboard tachs are a simple AC drag cup design.
I would test the 12v + and the neg of each guage until I found where the connection is lost.
think of it, if ya had 6 guages and the ground path was from guage to guage and the third guage in the string had a bad ring terminal which of the rest would be affected ?

 

[rodbolt]

Re: Reverse voltage??

sorry hit the post button to soon
normally the positive feed for the guage assys comes from the purple wire on the I terminal of the ign switch, the ground paqth is up for grabs, depends on who rigged it and what was going on that day.
I have seen about everycombination you can think of. the most commen is a ground buss on a fuse block.
the engine you can normaly rely on the engine service manual. hull rigging? all bets are off as most of it is done by minimum wage monkeys.

 

[Texasmark]

Re: Reverse voltage??

"Ain't no way" I'm a gonna get inna the middle of dis. Pie are round and cubes are square........if you only look at one side.

Mark

 

[Silvertip]

Re: Reverse voltage??

Sorry Dudes: That is not a series connection and daisy chaining is not used interchangably. You need to distinguish between the wire and the loads. The wires are daisy chained. The loads (the gauges in this case) are not in series. Look at the generic boat wiring diagram at the top of the "Electronics" forum. The lights, +12V and ground lines connect at the first gauge in the string and are paralleled down the string. You can lift the connection off any terminal and only the gauge on which the wire is lifted will fail to work. You will also note the two wires (the in and out) on each gauge are in a common ring terminal. If that were indeed a series connection you would lose every gauge after the one you on which you lifted the wire. And in fact, if gauges were wired in series, not a one of them would work. If each of those connections was in a separate ring terminal, then lifting one will kill the rest but that is still not a series connection. Two three or four batteries are wired in series to create 24, 36 or 48V. Gauges are not wired that way. Like I said -- picking nits, but lets use terminology correctly.

 

[guy74]

Re: Reverse voltage??

In my work the terms: Daisy chained and Paralleled are interchangable as Silvertip says.

 

[tomxdana]

Re: Reverse voltage??

If anyone is interested about the original problem. Started taking stuff apart to see how things were wired. The positive wires under the Battery Stop switch were real loose. Tightened the nuts down on the switch and everything was back to normal.


Thanks again,
Tom

 

[Silvertip]

Re: Reverse voltage??

I'm about ready to shut down for the night but before I do I want to add one last bit of discussion on the series/daisy chain issue to ensure this doesn't get out of hand. As most of the regulars on these forums know, I like to be the devils advocate in some of these discussions and the reason is to get people to think about what they write so that what they write is really what they mean to say. Bhile's comment that sparked this debate is as follows:

"Gauges often have a common ground and are wired in series."

See how easy it is to argue that statement. The intent was good, but the statement didn't portray the real message. While it is true the gauges have a common ground, they are not wired in series. Series and parallel wiring pertains to loads. Common ground is another point of contention. Gauges MAY have a common ground but I've never seen a boat that did. Common ground means the ground terminal on every load is routed to a single ground point in what is more commonly called a "star" configuration. In other words, every ground terminal on every device in the boat would be wired back to the ground bus on the fuse/breaker panel -- not to the ground point on a previous device in a parallel string. Since that involves a lot of extra wire, shortcuts are taken that are perfectly acceptable practice in 12V systems but it does cause grounding issues due to the multitude of potential loose/corroded ground terminations. Common ground (star grounding) configurations in electronics is done to prevent the kinds of grounding issues we see in the marine industry. Daisy chained (or series if you must) do not a common ground make. Good evening everyone. I feel better now!

 

[Barnacle_Bill]

Re: Reverse voltage??

Good grief!
Electronics 101: http://www.electro.fisica.unlp.edu.ar/temas/pnolo/p1_OIT.pdf

 

[achris]

Re: Reverse voltage??

In my work the terms: Daisy chained and Paralleled are interchangable as Silvertip says.

Sorry guys, in computer busses daisy-chains (which is where the term originated) are series. Break the chain at any point and all devices 'downstream' are disconnected.

In the case of boat gauges they are not daisy-chained, they are in parallel, or should be. That is, you should be able to disconnect/remove any gauge and it will have no effect on any other gauge.

P.S. Silvertip is spot on with his last post....

Glad you found the problem tomxdana.....

Chris............